Try out Shift 2, there's quite a lot of customization. Honestly there isn't much in the way of tuner games. You can try out Juiced 2: Hot Import Nights. You're far better off on a console for these games. Midnight Club games are sick.
You said you wanted upgrades but im still going to recommend the burnout series. Paradise is the only one on pc it is pretty good but if you want one of the best racing games to play with friends the burnout series on consoles is perfect.