Dafydd, well put. I was going to write along these lines myself but you have done that. The NZ system works well. Register everything VH and just have two classes, single and two seat. All ultralights in NZ have an annual inspection done by an Authorised person like a L2 etc. there is usually no cost for this. Insurance is covered by the owners. Two seat ultralights can be used for training if they are powered by a certified engine so even club built Rans S6S etc are used by clubs. As the ultralights are ZK registered pilots with any licence can fly after the normal conversion and not just holders of a micro light cert. there is now as I understand it NO requirement to belong to a club / association.
MTOW's are as per factory built/LSA or designer for kit/plans built up to the NZ max of 600Kg.
There is a annual "airways" activity of of $100.00 for all NZ registered aircraft.