I bought a Britrail pass back in 2002. In fact,I traveled from Edinbugh, London,Paris, Venice and Cinque Terre Italy, 2 weeks in all, never used a car.
If I wanted to go from Edinburgh, to a more rural area like St Andrews, I took the train to Louchars (sp) and a few moments later a bus arrived and took us to St Andrews. Public transport in Europe is plentiful.

If you rent a car, you then have to worry about parking it and paying to park it, gassing it (gas in europe is very expensive) etc.

For advise on rail passes, consult ricksteves.com or pick up one of his books and browse it at the book store. He has a free railpass guide, or at least used to.