You can crank the resolution on stepmania up as high as your monitor will allow, but I believe it will default to 640x480 (FYI, arcade 1st-4th ran ~320x240, and 5th-Extreme ran ~640x480 but interlaced, Supernova and newer can run 640x480 progressive if the monitor supports it, and DDRX and newer ran run at 1366x768 on the new flat screen cabinets). All the artwork will be rendered at the higher resolution. You can have some very crispy looking arrows if you crank the resolution up high enough.
I wouldn't generally mess around too much with trying to run these things in MAME. Last I heard, only 1st and 2nd mix worked well enough to be playable (3rd mix and later has some specialized hardware), and even then they rarely were properly synced. You can acquire the actual PCB set on ebay for ~$200-350. It's a somewhat specialized version of Konami's System 573 base platform.
The home versions (Playstation and Playstation 2) are fairly arcade faithful aside from having easier timing windows.
If you're interested in a low latency drop in IO solution including light support for Stepmania, let me know. I've got a board that is actually a drop-in for the real cabinet to hook it up to Stepmania, but it may be useful in other scenarios, as well.