If you have acess to dry acetone, it works damn well for helping precipitation of mesc hcl from dryish isopropyl (prob 95-97% in my case). Mesc hcl behaved the same was as you describe the acetates do, they'll precipitate and have to evap to get most/all of the xtyals, but still get the goo.
If you add dry acetone to your hot iso saturated with your mesc salt, it will start to precipitate without cooling. Mesc salts are not very soluble at all in acetone, at it makes them less soluble in the binary solvent as a mix.
I still had to evap, but i never froze, just heat/cool with evaps along the way. Collected most of the crystals, then evapped the last little bit of solvent, to get some crystals and goo/crap. Wash that and the xtyals separately with dry acetone (prob minimal amounts and cold if your using mesc acetate, not so big of a deal w/ hcl), then evap and save the washes, should be the crap/impurities/other alkaloids soluble in acetone.
Combine the crystals, crush lightly to not quite a powder, but sandy texture, then wash once more with dry cold acetone.
Took almost all the color/smell out of my mescaline hcl i thought was clean, after washing with dry acetone, and water re-xing, but i think precipitation out of alcohols gives cleaner crystals with less impurities caught up. At least while theres still a good bit of solvent, one thing to keep in mind is as you evap and concentrate the alcohols, the dirtier the precipitates will be.
I've also had ideas about using limo/heptane instead of acetone to force the mesc hcl to crystalize out of the saturated iso. But have not tried it as of yet.
Just take all this with a grain of salt as its ime with the hcl, acetates could have different solubility in iso/acetone.