I actually would recommend the upgrade, what microsoft says and what you will experience are different, as long as you keep good care of your computer and keep it clean, you'll enjoy your experience. Also, with the games you listed, you won't lag considering GTA is easy on the computer. I've ran GTA on a windows XP with 1gb ram and the worst possible graphics card you can imagine (Years ago,) changing the OS won't hurt.
EDIT: unfortunately your drivers may not work, so please make sure you have a backup handy from before you do the installation.
sometimes drivers that are only XP enabled may work for higher up versions of windows, but that just depends on luck.
make sure you have your drivers ready. http://www.dell.com/support/drivers/.../optiplex-210l