I never heard the 'original' z-plane filters, but i shure find those i have in EmulatorX pretty hot! I don't know what you didn't love in them, but playing with different filters shape, there alot you can't do in scope if you compare with those...
Using some of your older filters design spacef, like the vocal filter, you can probably get close to some in emulatorX (there's one called vowel pass for example) . Maybe it's only a design thing after all. Maybe you're right, that there is nothing to brag about in those z-plane filters. I still find them pretty usefull, great sounding, and use them in my sounds... They're better than what i have in STS3000 for that matter!

while keeping my DSPs for stuff that really matters, like a PRO12, Vinco, D-Master, etc...