I really don't know what managing a small team will teach Giggs about potentially running Manchester united. Read Keane's latest biography, the standards and expectations of any team outside the elite vary so much that what he will 'learn' will have absolutely no impact on what would be required of him at Old Trafford. These clubs are full of journeymen and have sub par facilities and a serious lack of finances. Even if he manages to do well with one of these clubs that will not prepare him any better for managing United than all the years he spent at the club and his apprenticeship under SAF and LVG.
This doesn't sound like a particularly convincing argument as to why Giggs should manage United. At least managing a smaller club would prove that he has an aptitude for managing a football club, which would give him a bit of credibility and legitimacy towards being considered for the United job, as to the coronation is undergoing right now.