OK, first off. Pertaining to MR2BAD's comments.
You said you run a 17x7 +42 all around, and use a 1.25 inch spacer in the rear. That's 32mm to make it close to flush! That should give you an idea of how tucked that wheel would be without the spacer.
In the front, you said you experience some rubbing on hard bumps. I can't imagine what is rubbing. With a 7" wide rim and a +42 offset, you can't even be close to the fender. The only thing I can think of, is maybe you have some negative camber, and you're rubbing the suspension.
I have 17x8 +40 up front with no rubbing problems at all!
OK, now let's pretend you wanted the wheels to be as close to flush as possible, with a staggered setup (what MR2's are supposed to have)
Ideal setup for an MR2 with 17 inch rims would be
F 17x8 +35
R 17x9 +35
Remember, this will require rolling of the rear fenders, so there's no rubbing on the fender lip.
Here's my setup:
F 17x8 +40 215/40
R 17x9 +35 245/40
As you can see, the rears are flush, and the fronts could afford to come out another 5mm. With the +40 offset up front, it also only leaves about 2-3mm of space between the wheel and the strut housing. Just enough to avoid any rubbing issues.
Now, you said you'll be getting a border kit and want to stay with 17x8 +35 all around. Since the border side skirt are pretty wide, you'll want to get as close to the fenders as you can.
The fronts will be perfect with a 215/40 tire
The rears will be slightly tucked. A 5mm spacer should allow you to stick a 235/40 on there with no problems at all. A 245/40 or maybe even 255/40 will also fit on the with no rubbing, but you might have to roll the fenders a little.
A 10mm spacer would put you perfectly flush with the fender, but rolling will definately be needed to get any tire on there, and a 255/40 will require almost completely removing the fender lip. A 245/40 will fit pretty well with good fender rolling.
So, in conclusion, here's what I'd do, if I were in your situation. Remember, this is only my opinion, you can do whatever you want. It's your car.
F 17x8 +35 w/ 215/40 tire
R 17x8 +35 w/ 10mm spacer and 245/40 tire and roll the hell out of those rear fenders!
With that setup, you'll be looking hot to trot, with plenty of suspension clearance!
If you actually read this far, GOOD LUCK!
Frank