The joy of crossovers is watching your favourite characters get rediscovered by your other favourite characters. Most fanfiction presumes a level of shared knowledge between all characters, whereas crossovers take that away. Sure, Sam and Dean know that they've both been to hell, but Captain America doesn't know, he gets to learn that for the first time! And we get to see his reaction! Yay! That's what we came here for, whether we realize it or not.
So, if that's what we came here for, then you want to draw it out. It's like eating a desert or having sex - yeah, you could do it really quickly all at once then roll over and fall asleep and it gets the job done, but I'd bet you'd have a better time if you slowed down a little.
Basically, what I'm saying is that you should avoid info-dumps. And you should avoid them for three reasons:
1. It gets the fun part over far too quickly. If Dean just sits down at the conference table and tells Cap all about his troubled childhood, his soul deal, his sojourn in hell, the apocalypse, Sam's health problems, and his confusing friendship with Castiel all in one go - we miss the delicious moments where instead Dean does something, or says something slightly odd, and Cap starts wondering "wait, maybe there's more going on with this guy than I originally thought... maybe this guy is a puzzle that I have to solve somehow..." and we get to ride along on the fun journey of watching him do just that. Likewise for Dean discovering who Cap is.
2. Dean wouldn't do that, nor would any other character that I can conceivably think of... nor would any real life human that I know. People, in general, do not want to talk about their troubled pasts. They don't want strangers to know their secrets (and everyone in a crossover is a stranger, unless you're writing a established-relationship crossover AU or a fusion AU). These days "How's it going?" is said as a greeting equivalent to "hello" where people don't actually treat it like a real question, and even if they do treat it like a real question, the automatic response is "good" (or "well" for the grammatically pedantic). People don't even expect you to want them to know how you are feeling THAT MOMENT let alone how you feel about your absent father or that time you were tortured in someone's basement. If you were to tell them that, and more, in a flood of information that was BARELY prompted, then you, my friend, are a weirdo. (I know this, because I actually do try to answer "How's it going?" honestly sometimes, just to see people give me the "I wasn't actually asking!" face - it's kind of fun... but I still don't talk about my troubled past or that time I was tortured in someone's basement...or whatever my equivalent is.)
3. It's just bad writing. Most of you audience is going to be familiar with both fandoms. They're going to actually know all this stuff. If you just present a summary of the canon in a big info dump, that's going to be boring for them to read. What's INTERESTING for them to read is how another character might react to receiving this information for the first time! But that gets taken away when you do a huge info dump, because then it's too much for the other character to process, what are they supposed to say? "Wow, that sucks"? Inevitably, when people do the info dumps, it's sometimes in a "who's had the worst life?" argument, so BOTH sides end up yelling big info dumps at each other in a game of one-up-manship. This is horrible because it means that BOTH parties aren't reacting to each other's stories beyond "how do I top that? Oh, I know - I was tortured for 180 years by Lucifer and my cock kills people!" and then after the argument, everyone just miraculously gets along because now they know everything about each other? That's no fun.
Anyway, my point is... bad crossovers annoy me.
PS: No, I am not writing a Supernatural/Avengers crossover - I just needed an example scenario and I didn't want to use any of the crossovers that I had written or may write in the future.
IN OTHER NEWS: My mum is coming to visit this weekend and we're all going over to the Island to see my sister, who recently moved there. So I probably won't be around - not that I've been around much lately anyway, but I will be EVEN MORE not around. I'll be back in time for the Supernatural season premiere though! Yay!