A 2012 survey by the FCCA (which is probably positively biased) estimated that an average of 74% went ashore with somewhat less when they had to be tendered ashore. With the Road Town pier under construction it is probably closer to 50-60%. I would estimate way more than 10% just at Cane Garden Bay.

Other factoids: Average spending in the BVI was $65.50 per visitor including excursion fees. 77% of excursions were booked and paid for onboard so the cruise line kept about 30% of that and the shore agent (Romney Associates) got another cut.

Once the cruise pier is finished it will be able to handle ships with a total capacity of up to 15,000.