The *.z80 snapshots should work as before: I have begun cleaning up and rewriting the existing implementation and added support for other formats, but the *.z80 code has remained unchanged apart from minor modifications.
Generally speaking, the ZX Spectrum driver shows a good degree of compatibility, provided the program doesn't rely on the features listed at the beginning of drivers/spectrum.c: if you find the keyboard unresponsive, maybe it's not MESS' fault: try changing the config switch from "Issue 2" to "Issue 3" (or viceversa).