Don't just limit it to MAME; NES emulators are readily available. ePSXe for PlayStation emulation, PS2emu for Playstation 2, mupen64plus for Nintendo 64, etc etc... It's great fun if you have a nice game controller for the PC.
Check out MyGaming Steam giveaways and
Donate it to a charity or school ect.
Steam OS is a waste of time at the moment...no where near ready for every day use.
Eat - Sleep - Overclock - Repeat