Big sway bars can make the car twitchier at the limit, and less compliant over curbs. Generally speaking the bigger the rear sway bar the greater the need for LSD. With an open diff, the big rear bar will pull up the inside rear tire and give us wheelspin. This is why on my "stock" MK2 NA I run a 15/16" solid front sway bar and the stock rear bar. I need that just to get the power down, even with the meager 5SFE. This tends to create understeer in theory, but in part the stiff front bar reduces body roll which in turn reduces camber loss under load, improving my front contact patch. Also, the rear tires are toed-out a bit to get it to rotate off the throttle. Probably not a great idea for higher speeds at the track though.
In my experience the stock '87 MR2 sway bar setup is pretty balanced. I went to big bars (ST front, H&T rear which I think was 19mm) for a while and didn't like it, so I went back to the stock front bar and no rear bar. There was an increase in body roll but the car was much easier to drive at the limit.
'Course, if we run stock springs, some stiffer sway bars are definitely in order to keep body roll in check.
We should add negative camber to the car as well, up front especially as the camber curve is terrible there. Stock you can get just about -1.0 degrees which isn't enough. -2.5 or so would be better. The best way to "hide" this is with crash bolts - much less obvious than camber plates in the strut towers (but also less optimal).
Perhaps for our LeMons MR2 we could run the ST front bar and a stock 85-86 rear bar (or two?).