Wait... RA-1s are 100 treadwear... if you have to stay over 140 to be legal, how were you running them? I'm guessing a rule or class change?
If you like the RA-1s, my thought immediately jumps to the Toyo R1Rs.
Of course, my immediate thought, which is probably totally wrong, was a high-performance all-season like an ECSTA ASX. You'd give up a little in terms of dry performance, but it seems like a much better tire for the less-than-optimal conditions. The thought of driving my RA1s over gravel makes me shudder.
I don't know Miatae enough to suggest sizes, my overly generic recommendation would be to run as light of a wheel that's large enough diameter to minimize sidewall slop and wide enough to run a tire that still gets you good enough footprint at 100-110% of the wheel width. (I know, duh, right?)