Just an amateur's theory......I think it depends on what condition your cards are in. Prices for cards in "average" condition, across all eras, have actually not risen significantly since the baseball strike in '94, except for a few very notable exceptions, like Mantle, and a few sets that for some reason capture collectors' interest for a period of time. (thinking of Cracker Jack) But a raw, VG '57 Yogi Berra, for example, is a bargain today compared to '94 prices, as is a t206 common (thanks primarily to the internet). And many post-war sets are actually cheaper today than if purchased in '94.
The real big money is in the high grade PSA stuff. If I wanted to selectively maximize my investment today, I'd sell my highest graded cards - no matter the era. Any HOF'er in a PSA 9 holder purchased raw, decades ago, is the equivalent of having purchased Coca Cola stock in 1910. The rate of return is so great, I'd never regret having sold them. And these are the cards most likely susceptible to downturns in the economy. So if your post-war collection is loaded with high-grade stuff I'd sell those.
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