a good quality amp with 40~60WRMS per channel would be ideal. you could justify anything from $300~800, beyond which i'd say you're overcapitalising.
for car audio, like home audio, having the sound 'infront of your ears' is ideal, and not from behind. as such, rear speakers don't feature highly in most enthusiasts' systems. however, each to their own, and many people enjoy sound from behind (i find it unnatural).
in the scheme of things, i consider the type-Rs as decent midspec level speakers but nothing outstanding. having said that, they're good. it's pretty easy to make good speakers, and much harder to make really great speakers, so at this pricepoint, they're few and far between. you'd need to spend significantly more to have significantly better.
