Old samplers like this are interesting, IMO, for sampling with and doing odd things like low sample rates for aliasing, extreme filtering, overdriving the input, corrupting the RAM, extreme transposing etc. etc.
Using them to imitate classic synths or do your bread'n'butter sounds for composing is, as you say a hassle. Like, you could spend hours rolling your own multisamples but why bother when there are tons of great libraries out there, and powerful tools such as Autosampler (which is now bundled in Apple Mainstage)? My Casio VZ and CZ libraries were done with that. Granted, I did a lot of tweaking afterwards, and initially setting up the parameters for the right ranges took time, but it saves a huge amount of tedious work.
I've just picked up a Casio FZ-1 and I'm very excited about the possibilities with it. The internal synthesis sounds great pretty much straight away because it's so easy to overdrive the filter, and it is a very cool sounding filter. Totally unique design, it sounds like a warmer version of the MS20 filter. I'm installing the Lotharek HxC floppy emulator (no more floppies yay!) and the display is getting a new backlight.
But for "regular" sampling duties, Kontakt, Autosampler, Recycle, Structure Free and Pro Tools rule my world.