I have both a 4003 and a 4004, so here are some thoughts on each.
4003: Much more versatile than it's given credit for. It does the stuff you know from Rush and Yes, but it also has the sounds that Sir Paul used a Rick for, and much more. Dead sexy. Old bridge design can make setups annoying, but once set up they're stable instruments. QC issues are hugely exaggerated, other than some minor finish problems.
4004: Older versions had a different neck profile than the 4003, now they're the same (though RIC's production methods mean that there is more variation between necks than most brands seem to have). Address most of the complaints about the 4003 line by using modern bridges, humbuckers and a contoured body. Basic sound is often described as an angry P-bass, which is pretty accurate. Neck pup can be huge and growl or be deep and thud. Bridge can be sharp or smooth.