There are few worse feelings if you're a super hero fan than your favorite protagonist finally making the "big time" and joining a grade A super team, but during a down period. You know what I mean: the Justice League is going through one of those eras when seemingly anybody can join and thus your favorite getting a spot doesn't feel epic, it feels like an afterthought (I'm speaking to you, Blue Devil fans). Believe me, I live in (not really) mortal fear that Nova is finally going to become an Avenger during a run where they're letting any old B-lister into the group.
Now the nice thing about these down periods is they rarely last and usually somebody on the creative end comes along to make membership in the JLA, Avengers, and so on feel special again; Grant Morrison did it, Kurt Busiek did it, and so on and so on.
For fun and excitement (mostly mine), I thought I'd do a little exercise trying to pinpoint the first instance in the case of each of comics' four biggest super team franchises where they gained that member who signified, "Hey, we're desperate, come on down and get your signal device." The interesting thing is that not all of the characters I'm going to discuss are necessarily bad characters nor did they make bad additions to their respective teams, but there's no doubt in my mind that once they gained membership, for whatever reason, doing so became a little less special for a bit.
Let's piss some people off...
The Avengers: Tigra
I think the Avengers actually kept their credibility levels high for a good long while in large part because Stan Lee made that major lineup change so early on, swapping the big guns out for Cap's Kooky Quartet, and almost immediately establishing the feel that it was the Avengers who elevated lesser known characters as opposed to more well-known characters being needed to elevate the Avengers. This philosophy made a lot of oddball choices through the first 200 issues of the series make a lot more sense, whether it was a relatively new character like the Black Knight or a quirky choice like Beast. However, during Jim Shooter's strange tenure as writer, he brought Tigra in under circumstances that were less than ideal and damaged the team's cred for a bit in my eyes. Basically, Moondragon made a bunch of random heroes show up at Avengers Mansion and try out for the team because she thought they needed a membership drive (they didn't); when the smoke cleared, not only did most of the newbies take off, so did stalwarts like Yellowjacket and Wonder Man, leaving the big three of Captain America, Thor and Iron Man with founding member the Wasp and new recruit Tigra. Though Tigra would go on to be a pretty cool member of the West Coast Avengers, this came right after some middling years as the Cat and she ended up leaving after only a few issues, making the Avengers seem like a high school athletics team you could just quit if practices got too hard. This would begin Earth's Mightiest Heroes' slow descent into inducting the likes of Doctor Druid and Gilgamesh until Heroes Return brought back respectability well over a decade later.
The Justice League: Elongated Man
No doubt I'll take some flak for this one, but hear me out. In the long run, Ralph Dibny (along with his wife Sue) turned out to be a wonderful addition to the Justice League and ended up one of the team's most enduring and beloved member over several incarnations. However, that's because he's a great character; very likeable, very quirky, and not so big a name that writers couldn't have some freedom to actually do stuff with him. But, if you come at it from a more meta perspective, Elongated Man really had no business being on the stacked Silver Age Justice League line. His stretching powers are simply not that impressive and while he's a fine detective, Batman is the world's greatest detective, so he really brings nothing practical to the team in terms of skillset. You could make the argument that Green Arrow was fairly useless during this era as well, but he was popular enough to carry his own book off and on, something Elongated Man was not. So essentially Elongated Man busted down the door of DC's all-star team, breaking through their glass ceiling to become the JLA's first fairly useless and not really that bankable member who was just on the team because he was Barry Allen's buddy, a pretty nice guy, and people seemed to like him and his wife. Ralph Dibny is the guy you let on the company softball team because you'd feel bad if you didn't. Again, over time the decision to admit Elongated Man to the Justice League was a strong one, but there's no question that the roll call of "Superman! Batman! Wonder Woman! Green Lantern! Flash! Elongated Man..." feels a bit off and suddenly being in the JLA isn't quite as special and hey, suddenly they're in Detroit and there's a friggin' breakdancer on the team.
The X-Men: Rachel Summers
Since their whole gig is more being the kooky outsiders of the Marvel Universe and not acclaimed and respected like the Avengers, the X-Men get a lot more leeway in their recruiting efforts here, but at the same time, Chris Claremont always did a pretty good job of making the new recruits seem like they really belonged...until Rachel Summers. I've read pretty much Claremont's entire run of Uncanny X-Men, and I still can't figure out if during the issues in and around #200 Rachel was an official member of the team, a probationary recruit, an ally or what. I know that she hung around the X-Mansion, complained a lot, and was so powerful that it was annoying because you really didn't need Kitty Pryde or Nightcrawler when you had a cosmic telepath around. Obviouly you can see that the Rachel of that period irked me (though she grew on me during her Excalibur tenure), but I maintain she was the tipping point as far as joining the X-Men seeming like a big deal. Up to that point, Claremont was pretty meticulous about only adding a new member once every big moon and making it special, but Rachel's ambiguous status really muddied the waters and suddenly it was hard to tell who was and wasn't on the X-Men's active roster. In Uncanny X-Men #200, I'm pretty sure former big bad Magneto officially joined the team, but the roster was so fluid in those days of Rachel haze that it didn't really seem like much of an event at all. Wannabes like Longshot, Jubilee and Forge would all shuffle in and out of the X-Men following Rachel's weird stint, and to this day it's always tough to tell exactly what the set line-up of any given X-Book is; it's not necessarily a bad thing, but no doubt becoming an X-Man will likely never again be the big deal it was for Rogue or Shadowcat.
The Teen Titans: Titans West
When the Teen Titans first started, they felt like a very important team because the group was comprised of sidekicks to very important characters; they were very much a junior Justice League. The addition of Lilith here or Hawk & Dove there didn't dilute the pool all that much because you still had mini versions of Batman, Flash, Wonder Woman, etc. hanging around. However, in 1977 with Teen Titans #50, DC opened the floodgates of the obscure and unleashed Titans West on an unsuspecting populace that was barely buying the regular Titans book. Suddenly Doom Patrol hanger-on Beast Boy, barely acknowledged Hawkman sidekick Golden Eagle, second rate Bat Family member Bat-Girl and a dang caveman named Gnaark were all card-carrying Titans. Once more, this was ultimately not a bad thing, because it opened the door for Raven, Cyborg and Starfire to make the scene and New Teen Titans to ascend to greatness a couple years later, but in 1977 being a Teen Titans hardly guaranteed you entrance beyond the velvet rope when you had Hornblower and Harlequin waiting in line with you.