The top layer of laquer can suffer from the effects of the sun and road grime. The occasional light application of T-cut shouldn't cause too much damage to the surface, provided you don't overdo it.
One thing to remember before you do use anything abrasive on the surface is to wash it down first to remove any grit which is going to do more harm than good.
The Disco is a big vehicle, so don't expect to do the whole vehicle in one go, just do one panel at a time and take a break. A good shine takes a top quality car polish and a whole load of elbow grease.