...to visit the MLB Hall of Fame?  Is it worth a trip or just something to see if your in the area?
I live in CA and not sure if it's worth a trek accross the country without having other plans?

every time. Even without the Hall, the village of Cooperstown has a lot of history in it's own right and is beautiful. One time when I was visiting, they were playing Abbott and Costello's "Who's on First" on a closed-circuit TV. It was one of the most popular attractions there, and still hilarious!

interested in baseball, there are better places to go.

Great place to visit if you love baseball.  But Cooperstown is way out in the boonies, at least an hour drive from Syracuse or Albany...better than 4 hrs. from NYC.  Well worth a week-end excursion if you are vacationing in NYC, Montreal, or the Adirondacks area, which I would recommend if you are making the cross-country trek.  NYC and Montreal are both hobby-friendly, though the latter will probably allow you to stretch you $'s further.

Rochester (2 hours?). It's not worth it if you have no other plans.  It's like coming to L.A. from N.Y. to see a Dodger game and then going home.

You can also go to Niagara Falls. Lots of casinos just across the border and where there are casinos, there are providers.