While it's true that BBC3 is pretty dire, I think the same can be said of 1 and 2 which have several times the budget for their shows. BBC3 probably represents fairly good value for money given that, on average, they've turned out one good show a year over their lifetime. BBC1 would need to turn out 12 good shows a year to be the same value for money, and it sure as hell doesn't do that!
That being said, there's no reason whatsoever they can't can a few repeats and put the entire home-made schedule of 3 onto 1 and 2. Strip the repeats and the imports and 3 only has a couple of hours' programming.
Ah well, I'll fondly remember them for:
Monkey Dust, My Life in Film, Bad Education, Pulling, Being Human, Mongrels, The Fades, Nighty Night, Pramface (well, the first season), and The Mighty Boosh. Little Britain wasn't half bad at first too, but that sort of thing wears thin extraordinarily quickly.