I thought Routh was decent as Superman, but I didn't particularly like his acting as Clark Kent. Routh and Bosworth would have been much better served by a new take on Superman where the characters are young reporters just starting out at The Daily Planet.
I actually think that Singer's take on the Superman mythos might have worked great if he'd cast leads who were appropriate in terms of portraying a Superman and Lois Lane who have shared a long history together, with Superman having left and come back after a long absence. Imagine Jim Caviezel and Diane Lane in the roles and it's a very different movie.
I myself had no trouble accepting that it was a slightly different version of STM that was being followed up (with different actors and a different looking Metropolis), but I do think it might have been confusing for general moviegoers.
Going in either one of those directions you laid out probably would have been better. If I had to pick, I'd go for the first, with Routh and Bosworth as a couple of young reporters in a reboot. That way they'd grow and mature into the roles and not risk looking middle-aged by movies 3 and 4.
