With the caveat that I am familiar only with the ACT:
The OC has a responsibility to insure the entire property. That may or may not include paving and gazebos but in any case they don’t seem likely to make much difference to the overall property value. All such changes should be notified to the insurer who can say whether a change in premium is required. In our OC quite a few units have very substantial improvements. EG. my townhouse has a whole second floor that was not original. The budget has to include insurance. To levy other than in proportion to unit entitlements requires an unopposed resolution. Although an argument could be made that units with substantially increased value should contribute more to insurance the impediment to doing so is very high. Unit entitlements could be recalculated according to a new valuation each time a unit made some alteration but that is a major expense and again has a high voting threshold to do it. We have just ended up living with the fact that some units have increased value but among over a 100 units the effect on the overall valuation of the site is quite minor and does not make enough difference for anyone to be bothered trying to overcome the substantial hurdles required.