My 08 Sienna has the VSC and Traction lights on, but the button to turn it off doesn't do anything.

These light mean that there is a fault in the system. It could be that there is a tire diameter mismatch (especially on AWD models), it could be a transmission issue. In my case there was a bad sensor in the transmission, which was not too bad to repair. When there is something going on in the drive train the computer defaults the drive train to a safe mode which protects the transmission, but will hurt acceleration and in theory, handling. It also is a well-known intermittent false alarm on some models. I would suggest getting a OBD-II computer (like Blue Driver) and see what the error code is. And/or take it to a mechanic or dealer to see what the nature of the code is. Even a small engine fault can shift these off, again, to protect the transmission. The switch does nothing in this case, the dash lights are there to say that there is a fault in the drive system, and you are now in "safe" mode.