17's are not to blame in isolation for the altered handling characteristics as just sticking 17's on an E30 looks wank, so most people either lower the car first or at the time of sticking the alloys on.
with 17"+ alloys you have rubber band tyres, which give a more coarse ride quality as they have stiffer sidewalls so less absorbtion of ride. The harder sidewalls which have less lateral give also make for sharp feeling steering to a degree. However the consequences of the low profile rubber means you get little warning when it's about to break loose.
Because of the larger wheels and lowered suspension this adds to tramlining and the car gets fidgety on roads with a poor surface and the car sometimes wants to follow in the grooves of the road. Lowering will also enhance any poor steering/suspension components such as worn bushes and joints, which will aggravate any unruly behavior
The offset of your wheels may not also be correct for your car, also causing tramlining if the width of the track is increased
get it lowered a sensible amount with some nice 15's and it will be smart as a dart.
17's just look cool
) seem to 'ride up' ridges in the road. I want ot loose this fell so am going to get some 15"bbs. Who else finds that 17" wheels get 'draggeg' into imperfectiosn in the road more easily?! 
