[r33_RGSport]

Agree with stewy604 , just rough estimation, the 2 rear suspension itself will cost you about $1800/side. Still you have to get the required module, do the wiring, coding, etc. If you are lucky, then you will get it to work, if not, you will ended up losing money without getting anything.
The best bet is to sell the current car and get the one that you actually want.
Also, towing wise, it will depends on your sports car, keep in mind that the X5 towing capacity is not that high.
Even the Cayenne Base V6 model have higher towing capacity than the X5.