speedup

I owned a 2007 A4 and sold it to my friend. I want a more powerful one. Since my previous A4 is reliable, I plan to get a S4. I did some research and contacted some dealers online.
At beginning, I only considered the new car and autopriceshare dealers gave me a fair offer: 2014 S4 (quattro S tronic Premium Plus) Price 45974. Just yesterday, a local dealer contacted me and said he has a basic model of 2013 S4.
I need advices for two questions:
1. Are there any obvious improvements since 2013 model? if not, I may take the used one since the price will be better.
2. Are there any platforms to share or estimate used car's price? For new car, I could check what others paid in autopriceshare.com. Are there any similar platforms for used cars?

Thanks in advance, friends

DrGP

No big changes from 2013. Try Truecar.com or Edmunds.com for new car pricing. Autotrader.com for used. I as well as others will recommend that you get one with the Sport Dif. If buying used, a Certified car is preferable but not a deal breaker,