My travel agency does about 60-40. Many people split the trip up and do AC & Cayo or elsewhere on the mainland. But lots just go to AC. Some just Placencia. Hardly anyone just mainland (inland). Although while in Belize one time I did meet a couple celebrating their honeymoon at Crystal Paradise (Cayo) and were not going to any beach at all - but that is rare.

www.barbsbelize.com