Is your mini a core solo or duo?
I haven't tried Parallels. I use XP infrequently enough that Boot Camp is fine for me. VMWare is developing virtualization software as well. I would like to see native virtualization (ie: full speed) in OS X 10.5, but I doubt it.
Steinberg makes Cubase - not sure how that compares to Wavelab. For one, it isn't yet a universal binary (Cubase 4 apparently will be), so you'd be running under Rosetta. I currently use Sound Studio, as it's good enough for what I need to do. I prefer Wavelab's dithering, but it isn't worth it for me to reboot into XP just to dither, especially when I listen to the 24bit version much more than 16bit.