Yeah it's worth it, The front's are very easy to do, and the rears take a little bit more effort. Pioneers in the front for me and kickers in the rear. Sound a lot better than stock and not too over the top.
Crutchfield.com is the place to search.
example of the search for Infinity Reference which are very good too. Infinity Reference X REF-8602cfx 5"x7"/6"x8" 2-way car speakers at Crutchfield.com
Don't for get to get the Ford metra speaker adapters, I believe they come in pairs when you buy them.