I bought a UAD-1 card recently along wioth the missing precision mastering suite bits.
I cant say that it has made a huge difference to creativity, but where it has made a huge difference is in terms of subtle sound shapig to get me to the kind of sounds I am after.
Also at least I no longer have to waste time trying to polish a track (and usually giving up) with the junk that ships with cubase SX - I am startingto quite like the result I can get out the the UAD mastering suite and thats makes a huge difference as now its really worth trying to finish stuff rather than add to the gigabytes of partials
Am also very tempted by a poco at sometime as there some specific tc plugins I am after. Actually I think the two seem to be very good compliments to each other - modern+vintage.