I had tried to use the Intuos for a 2-3 years like you are saying and could never get the hang of it. I ended up biting the bullet after graduating and getting the 13HD and have not looked back. I wish I got something like that early on in college. Of course, everyone’s mileage may vary, but –
Compared to the cost of school, laptop, programs, etc, a Cintiq (even a smaller 12/13", a used model from Craigslist, or an off-brand like the Yiynova that some here have tried) is worth it if you are going the tangible product design route. Sketching is already hard enough. Do you really want an added barrier that makes it more unnatural? I would argue that the need to Ctrl-Z dozens of times takes away from the core idea of ID sketching and would get in the way of coming up with new ideas quickly, though it could be okay for some really tight renderings.
In the time being, I would not discount your original strategy – sketching on paper, scanning it in, and rendering there. The Intuos is a lot more forgiving for that.