SIL: You're right. U13s being successful at U14 challenge in the fall will not find the same level of competition at U13 challenge in the spring. However, you need to propose a tractable (i.e., clear, concise, and without room various interpretations) rule that SCYSA could implement for these situations. On the boys side, a similar case could be made for 93bridge and if we go back a year to 92cesa boys. I would argue; however, that 93cesa boys, while a good team with some potential are not at the same level as the 93bridge boys. My point is this, yes it's unfortunate, but you've got to give the administrators a simple rule that can be applied without subjectivity, otherwise they open themselves to all sorts of protests, and potentially lawsuits.
I couldn't come up with a tractable rule, so I think you're stuck with biding your time for the spring season. So what do you do? To me, you supplement your regular season U13 challenge schedule with extra scrimmages or friendlies against available U14s, continue to play up in quality tournaments, and possibly play U15 next fall while waiting for RIII play in spring of 2008. (I didn't see anything to prevent a U14 team playing up to U15 in the fall and forfeiting your U14 RIII spring spot, but I'd check w/ SCYSA to make sure.)