Talking about isolation feet - just got a SL1300G and as I was swapping places with its 1500C predecessor, I could not help but notice the massive difference. The 1500 feet are fairly stiff, to the point they can seem/feel solid/fixed. The suspension on the 1300G is pretty "bouncy" in comparison which I assume would help with microvibration and damping.
Now I don't think my TT has much vibration (it sits on a fairly chunky, wall mounted shelf and the speakers are front ported, with the closest about 40cm away) but it's kinda reassuring.
That said, I probably would not spend £150/200 on aftermarket feet unless I had a serious vibration issue.