I agree with you on the plays you mentioned. And I'd add that with an offensive attack that had a running back with his talent and experience, we'd have probably beaten B.C., as well (who we took to the end with the minimal experience/skill that we had).
So, we'd have probably won 5 or 6 games vs. 3. But we also wouldn't have been blown out by the mediocre teams. No way would we have lost 33-3 to Georgia Tech, 31-14 to Michigan State, or 41-14 to Air Force. We lost those games by those margins because we simply couldn't move the ball - that wouldn't have happened with Walker in the backfield. Those would have at least been competitive games.
Add all that up, and 2007 would have been much easier to stomach than 3-9 with such an ugly point differential.