To a large extenet it depends on the robot design:
4 wheel drive its next to pointless
2 wheel drive with wheels abount central possibly improve its ability to go in a nice straight line.
2 wheel drive with wheels at one end well I couldnt drive mine in anything remotely close to a straight line without a gyro.

It also depends on the control system and mechanics of your drive.

Best idea is probably build it and see if you need a gyro. Ie if your having trouble controlling it. If you dont need it to improve the control then its just more money and another thing to go wrong.

Richard Wenman
Team Mayhem