I went ahead and connected a CRT to the PC, and compared a few programs next to an A1200/1084 combo.
In brief, running the PC display at 100Hz, setting WinUAE for PAL/50 FPS, no filter, and no vsync seemed to provide the best quality. (Naturally, you will need to make sure everything is cleaned up on the Windows end of things to prevent hiccups.) While not 100% flawless, from the standpoint of an average user I think the results are acceptable. Some AGA demos (Impossible is one example) can actually be a bit smoother via emulation, as even an 80MHz 68060 (and possible Amiga chipset limitations?) is not enough to play them entirely perfect everywhere.
Pinball games seem to be a small exception, while they may look *almost* as fluid just watching the table scroll (especially from normal viewing distance), actually playing them is not nearly as nice IMHO. Also, you will not be able to correctly run a PAL demo/game at 60Hz and have good scrolling.
Just some casual observations from a non-expert... :-) While it's a hell of a lot of $$$ for that extra smidge of better scrolling, I think a perfectionist will be unhappy with anything other than an actual Amiga (especially a game or demoscene nut). As I said earlier in the thread, I use and enjoy both. I would have no problem running WinUAE exclusively (despite flaws) if I didn't have room for my computer hobby. YMMV.
edit -- Something I just thought of, I bet you could use Powerstrip to create some custom video modes with more "precise" frequencies for use with WinUAE, that might help dial in the scrolling a bit better. Something to fiddle with later in the week. :-)