I know the earlier X3s had some issues with the rear springs where the pigtail end might break off, so checking the suspension might be a good idea. Also check that the moonroof works well with no leaks or curious noises.

Warranty usually only covers things that are broken (as JCL mentioned), not really preventative maintennace or wear-and-tear, but if you want to try the two areas above, might work out.

__________________
2014 Mazda 3 GT: Ø Consumption: (click for details)