Possible workaround?
 

Why not tack the stud in with a bit of 347 rod?

Because of all the hardware issues turbo miatas have, I avoid removing them at all costs, and constantly remove turbos and manifolds as a tight assembly. I see no reason not to weld if you want to continue tracking. I can pull my EFR's compressor housing off in ~5 minutes, the CHRA about 20 minutes after that. Welding the studs helps the stud itself, but the hardware may continue to back off. Are your motor mounts stock or mazda comp? I forget. I feel like you had a hybrid setup, but I've looked at many miatas since then.

Motor mounts are the Blackbird Fabworx street drop mounts, maybe switching to a hybrid setup would help to increase vibration absorption. I also remember seeing a thread here where the sleeve in their BBFW mounts wasn't long enough, so the entire face of the bushing was in contact with the ears of the mount. That could be a potential issue as well I suppose, no idea what amount of vibration is "normal".

I'm not opposed to welding, had a hard time thinking of a reason I'd ever need to take the turbine housing off. If something goes through the turbine housing so hard that it needs to be replaced I'm probably going to have much bigger problems on my hands.

Track days is basically all the car gets used for now. If the hardware issues could be resolved I'd be very happy, the car is a blast to drive! But if they can't I'll need to consider other options like going back N/A (blech), switching to a Rotrex (belt issues? too many heat exchangers?), going N/A while saving up for a Kswap ($$$$$), or going N/A while I save for switching to a new platform (not that I know what that would be) followed by a part out.

First choice would be to keep the turbo though if possible.