Hey Chris,
It has been my experience that if I'm working with a single trunk style and allow it to revert to kabudachi (clump style) that it does take away from the strength of the older trunk.
Conversely, when it comes to clump style, abundant new starts tend to slow any activity with older trunks. So I keep aggressively cutting down new shoots as soon as they appear unless they're in a position to assist in the balance of the design.
I've found with quince to keep them actively growing is best, kinda like seniors in the human variety...they must use it or loose it.
The particular quince that started this thread bloomed. It was white and I must say I was disppointed. It transplanted well and reacted negatively to all the sun it was receiving, so I moved it to a spot that gets morning sun (east exposure) for half a day and it seems to have liked this spot better. Not an aggressive grower, but holding off any kind of heavy fertilizer till next year. In september will give a shot of bloom fertilizer to prpare for the next flowering season. The 5 starts have all taken but like the mother plant are not too aggressive.