GT is getting boring for me... Tuning is too straight forward... not enough "choice" in the process. For example, the more expensive part is always the best choice for every car. The one possible exception is turbo-charging which is a bit of gamble with some cars. Still, being able to select from several different cylinder heads and cams and rotating assemblies would take GT to a level that I don't think any racing game has reached yet...
Whichever one gets to this level first will be the one that gets my money.