I think alot of these problems come from designers using Pantone colors, which are really a special mix of pigments and not made up of cmyk.
Jim
We've been having really good luck with a spot color workflow through Onyx.
The profiling in the new version is great, but you do have to have a basic understanding of color mgmt.
The flexibility you have at the rip with spot color tools is great for finicky vector files that are effect heavy.
We've found that converting to cmyk from spots can throw tints and such for a loop.
I'd say the key to any useful color management is having some kind of process control in place first.
The trick is getting everything to a point that can be reproduced everytime.
A spectro and x-rite software isn't going to magically solve all of your problems.
We did a job for pepsi with over thirty spot colors in it!
Our profile saved us probably three shifts worth of color correcting.
We run grand format fabric, it's a little tought to replicate the process for a proof.
I suggest creating custom profiles to anyone...