IMO, upgrading domestic flights provides an even lower bang for the buck than redeeming domestic awards. What's more, you might be surprised to learn how much additional cash you need to throw down in order to upgrade your flights to Europe.

Nowadays, it's frequently possible to acquire miles on the cheap (e.g. with credit card sign up bonuses and promotions in which miles cost less than 1 cpm). By taking advantage of these, you should be in a position to top off whatever program you end up going with in order to redeem some high value awards.