Extremely impressed with the ride quality, essentially as good as (if not better) than the ride you would expect from eibach pro kits which I have used in the past.
I was very concerned about ruining the ride quality and regretting the install, also scraping on anything with an angle.. but the car looks better, rides the same as stock if not better (less roll) and I do not scrape on anything assuming I take steep driveways at an angle etc - I slightly touched that lower black plastic (wind difuser?) that sits really low when I deliberately tried to see what I could get away with in terms of not taking an angle etc.
So if your having any doubts about ruining the ride quality, dont.. I think if you dont want the ultra slammed look - RSR Down / RSR Half Down / Tein H Tech are all great options!
for the question above it does not effect AVS only removing everything / replacing (eg coilovers - which are now being designed to accomodate the AVS soon anyway), the workshop that did my install took approx 3.5hrs - could be done in less time but they asked if it was ok if they did not rush the job considering my car is essentially brand new / they havent worked on one yet - so factor that in, and factor in an allignment - they actually said after the springs were installed the allignment was better than what it was when it came in stock (nice one lexus) so i will actually get more wear out of my tyres now than before.. lol
If you want any more specific info re RSR Down's feel free to PM as I did with other members prior to purchasing