I think it's a great idea, except I'd recommend a proper dirt bike instead of a dual sport, mostly because dual sports tend to be fat pigs and that's not the best to start with imo. I think the best thing about dirt bikes as trainers for street bikes is that they help you keep a cool head when things go awry. You will lose traction often and typically ride very close to other people, both of these things are good emergency training for street riding, again just imho. The consequences usually aren't as severe in the dirt, but just painful enough to commit to memory.

