I highly doubt playing on an upright will improve playing on a grand. If this were true, then then other piano students would play superbly when they play on the concert grands since most of them practice on the uprights at school. But no, they don't. There are many things that learning to play on an upright will hinder a student including how to attack the keys, different pedalling techniques, and listening to the tone. The few who do have access to a grand at home, on the other hand, play far more musically are able to attain different varieties of touch, and have better pedal control, when they do play on the concert grands.But maybe it could be that those whe don't practice on a grand don't have the time to practice on the concert grand to get the feel for it yet...The touch difference you feel is because the action is far superior to an upright. Grand action can never be replaced and you'll be able to play much more effectively. It's is likened to driving an old Volkswagon Beetle and then driving a new recent model Beetle - there will be noticeable improvements in all areas. But don't expect that improvement to translate back to the old Beetle because it is not the driver but the car.
I really like your thinking, but I don't think that a formula one driver would benefit by driving my mom's corolla around the track...
you know..whenever i play on a grand..iplay worse..this is why i prefer uprights over grands...but maybe its just a phase