Well, I finally got the chance to drive a Mini-Z this week (stock MR-01 type) and now understand what you guys are talking about. My opinion still differs in some areas.
First off, the electronics, particularly the steering, is far more precise on the Mini-Z. I was having little trouble staying off of the walls on the track, where the XMods all tend to get pretty beat up. Turning radius is so much better. Overall, much easier to drive, but I was missing the brake function.
Proper tires were essential on the Mini-Z with RWD. The owner was using soft treaded XMods tires on the rear, and he cut grooves in the stock Mini-Z front tires. The car handled very well with this setup. Despite being an MR-01, it seemed less prone to roll over in the corners as well.
I tested the top speed of the Mini-Z on the Tamiya speed checker, and the car would hit 19kph, vs. 17kph of an XMod with a stage 2 drift motor or 21kph with a stage 2 drag motor.
The only issue I have with the Mini-Z is durability of the chassis, particularly the H Plate, which in fact broke on this one later on in the evening (No, I wasn't driving it at the time
) The Overland that runs there has broken a couple of times too. The XMods, OTOH, seem to only break axle cups for the most part. It doesn't seem like the body protects the chassis as well on the Mini-Z as it does on the XMods. Not to mention it seems to become detached easier.
Anyway, after that driving experience, you might see me go with the aftermarket electronics idea, or else I'll end up picking up an MR-02.