We have to pay harbour dues in Chichester Harbour, but this may be only applicable here
http://www.conservancy.co.uk/page/Harbour-Dues/319/The AI is is quite sizable when on the water and will always catch the eye of the Harbour Master.
Best check where you are sailing.
With regards to insurance, it is compulsory if I want to sail it from my sailing club and also it lives outside, so I have mine insured anyway.
The other consideration is that it can get quite a lick on and isn't the quickest turning thing on water. In the event of a collision, it would probably make a mess of some of the lightweight racing dinghies etc and they cost an arm and a leg! The racers at my club (several world & olympic champions amongst them) would not accept a repair to their hull, they would be after a replacement.
For the £80 quid or so it costs, I would rather have the peace of mind.