Long-time player (~'93) with decent collection.  I play Commander almost exclusively, and within that, I rarely use Search cards, Alt Win cards, or even that much Ramp, preferring accelerated card draw and letting the deck run on it's own.  So I have good old stuff, like Demon Tutors, that I've got no problem trading off for more recent things I like or for older things I don't have but that gone up in value.  For the older cards with value, I prefer to try to find other cards of similar value, b/c that's the only way I'll ever acquire them.

I *hate* foil cards (always have), and will trade my Foils all day.  Occasionally I will have copy of a card *only* in foil, and in that case my preference would be to trade for a non-foil version + something to cover the difference, but that's more a Guideline than a Rule.