I've been to Utila twice (Laguna Beach Resort is awesome; Newton boats, you don't have to touch your gear, laid back divemasters) and Roatan twice (Reef Gliders are also fantastic. I flew into SAP both times for Utila and am always amused by the tiny little flights from the mainland. If you're spooked on small planes or have a phobia of small spaces, it's not for you. But I actually think the tiny little open building of an "airport" and the runway with a dirt turnaround at the end are charming and part of the reason I love going to less populated locations. It was easy to get to Utila using frequent flier mileage on Delta and hopping over to SAP (from Minnesota it was easier than Roatan).
I was on Roatan in January 2014 and the daily public ferry to Utila was still unavailable as sadly Captain Vern was killed last year. So you'd have to book a private charter, unless they've started up again.
Have a great time on Utila!