The problem with Free Play on the Vs. System is that there's no attract mode as a result.
For example, I currently have Excitebike and SMB running and both sit on the Press Start screens if I set them to Free Play. If you get Game Over, it goes back to the Press Start screens. I just keep them on Coin-Op mode. One quarter can last a long time depending on what game you play, so it's no big deal.
Eventually, I hope to run all my games on tokens, but to each his own.