The solution to this to me is simple:
When you take entries, they enter one of a single breakdown of categories:
- Solo
- Teams
That's it.
On the entry form, you ask for DOB, Gender, whether they're riding singlespeed for each member of the team. And you tell people that as organisers you'll form categories based on what has an appropriate number of entries. This whole thing of catering for people who won't race just because they're not competitive just because they choose to bring less gears, or because there has to be a category they know they're capable of finishing top 3 in is just lame.
If you get only 3 teams of 3 entered you just don't split out triples. Only got 2 riders over 40? Easy, you don't split it out into 40+. Got 50 singlespeeders? Great, give them a category they deserve. What's that, the breakdown of solo riders is 30 riders aged <30, 40 aged 30-39, 20 aged 40+? Sounds sufficient to offer Expert, Vets and Masters on top of Elite being the overall.
For an 'Elite' event where you want to offer cash prizes in particular categories this doesn't make as much sense, but when you're holding a 'participation'/fun event where you don't want that kind of atmosphere, this makes total sense to me.