How did the sound change? More detail etc?
I fitted the top plate and sub chassis at the same time so I can't isolate what did what. But the effect was big. Very big for the money it cost.
Overall I'd say it was cleaner and clearer. Less hash, a lot less hash. The deck has an AT OC9 MLII on it and it was quite fierce at the top end. Afterwards it was very clean and well behaved.
Did it alter the sound? Yes, otherwise I'm not sure I'd see the point ;O) But I'd say it was wholly for the better. The deck was more tuneful and enjoyable. Even my wife commented on how nice it sounded and she doesn't usually notice these things.
The top Rega arms are still neutral but not in the dull way the older, cheaper arms where accused of. They keep the neutrality but add detail and dynamics. Very nice arms. The newer budget arms are also better than the older arms. As you might expect.
I don't see couloration as a problem myself. In fact I think a system needs it to give you a lively, life-like sound. Too clean is too boring.