Mine had 53500 on it when I sold it and although it was cheap, excellent nick, spec etc, it took 4 months to sell! I reckon about £30000 for anything upwards of 25k miles is a thing of the past now for the GS unless it's an mc victory or something very unique about it.
Try telling that to people selling!
Personally, I dont think GS pricing can be generalised they are just too dependant on history, spec and colour combos.
A 30k mile LE in nice colours with good history are not too common, let alone with price tags of £30k, either privately or at independants. In July I viewed (and, arguably, foolishly walked away from) a 2007 one owner LE with 26k miles, FULL Maserati history, just had its 31k service and new disk/pads all around for £32500, including a £1500 warranty from GrayPaul in Nottingham. Of all the cars I've seen, that was the standout for value. It was Blue with blue/black interior and while a lovely example, it didnt do it for me.
Since then, I've seen older lower spec cars for thousands more - where's the logic?
Personally, I think if you snagged a 2006 LE with nice colour/spec/history for c£27-28k with 25-30k on, you've done allright.