plenty and then some for MAME, and pretty much anything up to and including Dreamcast/Naomi.
While you probably don't have a spare lying around, an SSD is a great bang for the buck add-on. Even a $20 128GB SSD to boot the OS, and run your front end (with all the pics and videos that have to load in real time), and maybe your MAME roms, if they fit. Makes a huge difference for the cost of a trip to McD's for two.