Yeah, keep the tank. I still keep my oem Chinese tank even though it only good playing on smooth surface. It have rubber tracks which can easily come off when maneuvering on the carpet & grass. I'm planning to painting & weathering it.

If you must upgrade, upgrade the electronics first. It seems speed is the main problem. I'd do it if it's not expensive.

Btw, can you easily get spare parts for your tank over there, especially tracks?