It could be a good idea if you have greatly improved, BUT, if they are selling really well I would be careful.
You have a good search ranking BECAUSE they have sold well, and they continue to sell well because they are now ranked high.
If you upload competing clips that some people choose over your best-sellers, they might lose their ranking over time and you will stop getting sales.
There is no guarantee that your new clips will replace the sales of the old ones. The competition could be much higher now, and you might not get as lucky with the new clips.
If the clips sell very well, as you say, then one would assume that the grade is good enough, no?