I've skipped through Eric Jordan's book on Modern Commems
http://www.amazon.com/Modern-Commemorative-Coins-Invest-Tomorrow/dp/1440212899I still need to give it a more thorough reading. I think Key dates/mintage numbers are of utmost importance, but good/desirable designs help. That said, I think one of his pieces of advice is not to try to guess on any specific issue and instead collect the whole set. With silver skyrocketing, all of the numismatic premium on the non/semi-key coins is going to get swallowed up by the metal value. Not necessarily a bad thing for someone holding a lot of coins, but not the ideal way to invest (just buy bullion).
Rough example:
Assume the Lincolns are going for $50 and generic commems are $30 today. When silver hits $50, those Lincolns are still probably going to be around $50, but now the generics are nearing $40. Your investment in Lincolns did nothing for you gain-wise.
Another example is the 1982 George Washington commem half. Same 90% metal content as a circulated 1964 Kennedy, but much prettier and even has a proof version in a nice little box/capsule--but it goes for the same price or less. People do not know it is 90%. I love snagging these things on eBay for well below spot.
Again, I'm sill learning myself, so DYODD.