I don't think a company ever acquires another company because they feel bad. If they want to buy you it means that your company could play an integral part of their strategy. If it seems like they think they're doing you a favor then that means they are trying to low-ball you and you should ask for a higher price.
Yes, if you limit your dataset to "every great startup," then, yes -- you should go back in time and bet on them when they're still an underdog. Whatever that means. Go back and bet on Google. Become employee #1 at Facebook. Buy 10% of Twitter in 2006.
Probably, maybe, possibly?
Hard to be sure either way, indeed just as hard as when you're thinking about buying them.
Speculation is never very useful after the fact :)