I disagree with kremit, but only by a hair, and tentatively.
This is actually a tough question.
If, say, you go to a 16 x 7.5" wheel that weighs, or 15 lbs or so, you could mount a wider, stickier tire with lower profile, and you will notice much difference in handling, braking, accelerating, and steering response over your high-profile, squirmy little tires.
And then you will also notice the limitations of your suspension.
If you upsize to heavier wheels, though, you'll kill it.
Tires are the first thing I'd change on a vehicle, but there just aren't any really good performance tires in 70-profile.
