We were glad that we weren't there between Christmas and New Years, as I suspect there is so much traffic then that mooring balls may often be filled to capacity. But outside that, it's probably a crap shoot with pretty good odds. Maybe someone who lives there can fill you in better. As suggested, yes that Christmas-NYE time-frame is VERY busy.
Don't forget that overnight mooring ball rental is a business, and if there's sustained demand for them, then there's an economic incentive to put more in. This might make the anchoring folks unhappy as they see their free anchoring areas encroached, but it's good for the environment since it protects the coral better than people dropping anchor all over the place.
I agree with the science that in delicate areas fixed moorings do less overall damage than boats coming and dropping anchors for the night. But as one of the "anchoring folks", who happens to be local, I DO NOT anchor in live coral or on grass. If I can't get to a large patch of sand, that I know is there because I've anchored and/or snorkeled there already, I grab a mooring ball. So keep in mind there are many of us who are aware of the the coral and we are not dropping anchor all over the place. You might also consider the economics as well. Grabbing a mooring in the BVI is $30/night. Not much really if you are on vacation for a week and you've spent thousands on a charter boat and airfare. Look at it another way for locals and cruisers. That mooring fee becomes $900/month, or almost double what I pay for a slip with electricity/water/bathrooms etc. I already have a slip for my boat that I pay for whether I'm in it or not. When I have very good ground tackle and local knowledge, why do I want to pay $30/day to be tied to a mooring? That same mooring contract you sign at payment states that they are not responsible for any damage caused by their mooring failing. Some used to state that if there were high winds you had to leave. I do not have empirical data but I do know locally of far more instances of boats being damaged that were connected to mooring balls than were connected to their own anchors. Anchors typically drag, giving some warning if you are aware. Moorings typically fail completely and sometimes silently.
This BVI anchoring/mooring idea has been fodder for much debate amongst my friends. It goes something like this:
1)Do you think there are more and more moorings because the seamanship skills of charter guests have declined and they are willing to pay the fee for simplicity?
2)Do you think it's just another revenue stream with the benefit that they can pack more boats into a smaller area?
3)Moorings are installed to protect the environment? Would now be a good time to bring up the subject of holding tanks and pumpout facilities?
I happen to believe #2, I wish it was #3 but hope it is not #1.
Last but not least. I enjoyed your balanced trip report. I've read hundreds of these things and frequently you get the "everything was perfect, we were surrounded by dolphins and rainbows and the wind was always on our beam...." or "the knob on the drawer under the stove was loose. I only needed to open the drawer once during my trip but it sure was annoying. I had to call service to have the screw tightened a quarter of a turn and I waited almost six minutes. I will never use ABC company again after they refused to give me a full refund and comp my next trip!!!"
I'm always glad to read about charters who know how to sail in brisk winds like what you described. Many never raise their sails and only motor or are horribly overpowered flying full sails because they do not know how to reef.
I hope you come back and sail here again.