Jonathan,
Yup, we're back to the ShopSmith analogy again: anything designed to do multiple tasks doesn't do any one of them particularly well.
While I'm not usually a fan of digital, digital multi effectors have been around for a long time. Like my old Yamaha, most of 'em have some decent effects, but not all of the effects are decent or useful. They all usually add a bunch of noise as well. Despite the Yamaha being digital, it has an awesome distortion, but you can't combine it with anything other than what the factory programmed, and it does add a bunch of noise (plus some digital artifacts as well). I won't even talk about the hassles of real-time effects program switching, either with MIDI or a sequential footswitch. Analogue multi-effects are usually just pedals put in a common case and suffer from tone suck-out and noisiness...and you can't necessarily change their order in the chain. Modeling effectors which are all the rage today are just newfangled digital processors with fancy algorithmns that try to approximate the real deal. Some, like the Vox, have a tube or two in the circuit to try and HiFi' out the sound, but you still have those craptastic digital approximations mucking about with the sound. You know, like equal or splenda trying to approximate sugar, LOL! Close (?), but no cigar, LOL!
I've found that the only way to truly approximate a Marshal stack, for example, is to play thru a Marshall stack. Just as good as usually isn't.
Pete tries to take the best-sounding effects (usually analogue) and make them as noise-free and least harmful to tone as possible. A noble fight...it works for Gilmour and Co...hopefully, it'll work for you as well without breaking the bank.
Good Luck in your quest for the Holy Grail of Tone, I'm envious and, for now, will have to live vicariously thru your efforts. For now, I'll jut have to live with a simple guitar thru a hi-quality cable into a tube amp(s) until I can get my hands on something that sounds good without all the minuses associated with guitar effects.
Cheers,
Kevin