should not be a probelm . . .
It's definitely possible to upgrade wheels and tires and keep the same (or close enough) outside diameter of the tire.
The suspension geometry is designed for a certain tire diameter, so if someone were to increase or decrease the tire diameter enough with no other changes, then the suspension geometry changes and could account for things like bushings wearing out prematurely.
That doesn't seem to be the problem in your case. Your car already had 17's and I don't think a half inch increase on the wheels with the same tire size would make too much of a difference. The wider wheel should allow you later to go to a wider tire with a lower aspect ratio (in your case 45 down to 40) and keep the same overall tire diameter.
Any other suspension gurus out there got any ideas?