Not at all. We already have an aggressive 19" setup. The small reduction in wall height with the 20" would be minimal. The 20" upgrade is a very good wheel size for this car.
The D3 springs make a great compliment to this car and make it look it's best. Ride quality depending on who you talk to is anywhere from more springy/softer to more aggressive/rigid. IMHO I lean towards describing the ride quality as the sport ride of the Mag Ride setting. You will get one pair of fabric spring sleeves for the top portion of the front springs with the kit, but if you ask James nicely he just might include an extra set of sleeves free to install on the bottom portion of the front springs. I recommend this because as I have found, having done this kit with two V2 cars already, that the extra sleeves eliminate squeaking caused the painted coil contacting the lower rubber perches. The rears don't need them. Good choices in my opinion.
It also depends upon the tire size too, as this relates to the pressure needed to handle the load. There's the suspension AND the tires that absorb the shocks. The sidewalls flex, bending on bumps. You can see this by jacking the pressures way up, and returning back down low to normal. The springs are shorter, BUT have a higher spring rate. This also means that they won't flex as much on a bump too. If you live in a bumpy area, I'm guessing you will notice changing both things.