The "only 5 point" increase as a percentage of the base is a 50% increase for U.S. citizens and most others. The increase for Commonwealth citizens is 300% -- from 5 to 15%. Guess a 50 to 300% increase is nothing for "professional" real estate investors and wealthy Belizeans, but for ordinary folks it seems fairly substantial.
As to whether it will make a difference in sales, I'd say time will tell. I've personally heard from about a dozen would-be buyers today alone, mostly Canadians, and they say they are thinking twice now about buying in Belize, but maybe they will change their minds.
If the tax money goes toward professional real estate licensing regulation, I would be very surprised. I suspect the money will go to paying debt service.
Belizean real estate taxes currently are low, but as I say, if Belmopan can raise real estate transfer taxes on gringos by up to 300% in one fell swoop, what's to prevent the politicians from raising real estate property taxes on foreigners by several hundred percent tomorrow? Or imposing a capital gains tax on non-citizens?
Foreigners don't vote and, unless you're a Lord Ashcroft, have little political influence.
--Lan Sluder
AmbergrisCaye.com 
