MrDizzle, from the standpoint of being a toy collector in general myself, I strongly advise you to reconsider selling anything. I'm speaking from personal experience here...I've sold several collections over the years. Sometimes it's simply been due to the fact that I was bored with a given line, then other times I've sold things to be able to afford other things. Nine times out of ten I've always regretted it though. I've always come back to the realization that I've bought things for a reason. It either appealed to me because there was something about it that either spoke to me and I just thought it was cool, or it brought me feelings of nostalgia if it was something I either previously owned or was a reproduction or resembled something I'd owned in the past.
From the perspective of being a Marvel collector, I'm not so sure my opinion would be very valid. I'm new to the Marvel Legends/Universe/Select collecting game. I just started in earnest back in the spring after flirting with the notion for years and buying a figure here and a figure there. It's still new and exciting to me, but I can understand guys like you that have been in the Marvel game for decades and are experiencing burn-out.
Having said that though, I also want to reiterate what Dragon said: my Marvel collecting has been very fluid and unstructured...there's not been any goal set for what I want and no mission statement like we as collectors tend to do when we get turned-on to a given line. Like I said, I'm relatively new to collecting Marvel figures. Now I've had superhero toys since I was four or five, pehaps younger even. And over the years I'd sporadically buy a figure or two here and there. But I really started devoting real time and money to Marvel figures back last spring. I hadn't bought many Marvel comics in recent years. I used to be alot more serious, but for some reason or another, I just got away from it. But I was very impressed with the Iron Man movies, which allowed me to truly appreciate the concept behind the character. That, in turn led me to seek out Captain America: The First Avenger, Thor, and Hulk respectively (although I had seen the first Hulk film before), so naturally I was suddenly intrigued with these characters, and of course, The Avengers. It just snow-balled from there. Turns out I love Captain America and can't get enough of the character, and The Avengers may very well turn out to be my favorite movie of all time, and that's saying something since I'm a huge movie nut. And all of this of course has led me to seek out anything Avengers-related, then a few select Marvel characters simply by pure association that I've always thought were cool, like The X-Men, Daredevil, and Spider-Man.
I gues what I'm trying to say is, I've just been collecting stuff as it comes along and enjoying myself. I didn't decide one day that, "Hey...I'm gonna start collecting Marvel figures, and I'm gonna own the ultimate collection. Where can I find the most comprehensive checklist out there?" I just decided I liked the Avengers in general, then I looked at everything was out there, and what appealed to me personally. And I've not necessarily hunted high and low for stuff. I mean, I'll look for stuff, but I won't really go out of my way, and my collecting has been so much more enjoyable when I've come to the realization that I'll live if I don't find certain figures. For example, I want the new Marvel Legends modern Thor, but every time I've found him, the paint's been sloppy, so I've passed. I want it bad, but I don't have one, and that's okay. I want the Face-Off Cap. Will I own one? Maybe, maybe not. It's okay if I don't. I'm just taking things as they come, literally, and I'm enjoying the hobby so much more these days for it.
It's like the other day...I stumbled upon the Marvel Universe three-pack that has the Red Hulk, Iron Man, and Thor. I had no idea this set was coming out, but I've been wanting that particular Hulk sculpt really really bad, and I just find the Red Hulk interesting. I don't why he's red (lol), but he's cool-looking. Incidentally, I'm finding myself loving the character after so many years of dismissing it as a one-note character full of rage and not much else. I'm learning that's not the case, and the more I learn about him, the more I love the concept behind it. Anyway...I didn't necessarily care that this set also comes with an Iron Man figure I already have, and a repaint of a relatively common, over-used Thor sculpt. It's three of the Avengers!! It's just cool to me, so I put it in lay-away with a second set and a 6-inch movie Loki. My point is that yeah...I'm out there looking for Avengers-related stuff, but I'm not killing myself or breaking the bank, trying to get my hands on every single thing, just what I happen to find and/or think is cool. That's the key to enjoying our hobby I think...decide what you want, get it, and if you can't, it's alright. The sun will still come up tomorrow, and you can simply enjoy what you do have.