Don't do it. Buy what you like so you won't feel cheated. Be prepared to lose.
While playing the current era market is sometimes (but not always) a minefield, those who invested wisely in vintage baseball cards over the last couple of decades did well--as long as they followed some tried and true ideas.
Not everything is a home run, of course, but the fact is that the vintage card market does sometimes act like the stock market. Far fewer card players are involved but they're the ones who've consistently driven markets higher through the laws of supply and demand.
Business Insider talked with PSA's Joe Orlando and others for a feature they're running in their Financial section today on investing in baseball cards.