The new 6 is nothing special. If it was the EURO or JDM version then we are talking. One of the versions that we do not get has a 200+ hp turbocharged engine. The one we have here is just a normal 4 door. The thing that sucks about a new car is that the only thing going for it is that it has no miles on it and well is new. It is slow as hell of the lot but it still cost a shit load of money.
What do those things go for?
What year is your si?
If it is a 5th gen then i say keep that, and with the money that you were going to spend, have a shop build you a beast (or you do it yourself) Calesta had some shop build him a b20vtec for 6k, talk to him about that. Then with the other money that you were going to spend on the car (20k right?) impove the suspention, brakes, wheels and tire. If you still want to spend some money, do weight reductions, (CF hood, fenders, stuff like that) and then paint them (dont leave cf stuff black paint them so they match your car) and maybe some interior stuff like improved seats, and stero. If you put that money towards your car, you will fly by any new car.