The Water Taxi experience is fun, but not for those who are in a hurry to "get there". You probably see the water route to the mainland anyhow on one of the many mainland exursions available on the island. Seeing how getting to your resort will be an all day event, you may want to just get the puddle jumper to the island.
I recently jumped on a boat full of Costa Maya guests going up to the mainland for Cave Tubing, The Zoo, Zip Lining and the ruins. The boat ride over to the mainland and up the Olde Belize River was tons of fun, my first time going under Haulover Creek Bridge. It was a much better route than going into the City. Everybody had a great time!