I'll take a gamble on old stuff if shows some promise and it's cheap enough. I've done well with E-6 up to 25yo, given that new film is $5/sheet. I have a bunch of Acros, which Fuji says should have no or minimal degredation with room temp storage for 1-2 decades after the expiration date. I happen to really like how Acros looks in comparison to some newer tabular grain films.
I have a box of Royal Pan that was sold to me as hopelessly fogged, but dirt cheap. I've gotten better results than the seller described, and when I feel like fooling with it, I think I could do even better than I have. My next step is probably going to be benzo in chilled DK-50. It's an experiment. We'll see.
However, I've been happy with newer films, and I think the prices on Foma and Ilford are pretty hard to beat. So that's kind of the limit there. I can't really see buying old Tri-X when I have new Tri-X. Or old Plus-X when I have new FP4. Or any of the older finer grained films when I have newer TMax and Delta. I get that the formulations and performance aren't the same, and aren't even constant for the same product over decades. But neither will performance of old film, and I'm not trying to reproduce any prior result.
I guess what I'm saying is, there's sometimes an economic argument to taking a gamble with some old film, if it's cheap enough and newer film is expensive enough. Or, there's a curiosity argument in that it's sometimes fun to see if you can make something work. But I don't think there's a fantastic photographic argument, and I don't think new B&W film is particularly expensive.
