J,
How can you say "it's not really any different"? If you actually travel and fish tournaments why you wouldn't spend the extra money on a diesel is beyond me. I have owned and towed with 3 different vehicles in the recent past here is my experience:
1) Ford f-150 (150k miles) - Blew while towing up hill, less than 10 mpg while towing
2) Ford Expedition (120k miles) - Transmission gave away and motor begin to miss/bog down. less than 10 mpg towing
3) Ford f250 7.3 Powerstroke (118k miles) - Never had an issue, stays under 2500 rpms while towing up Tennessee mountains. to many benefits to list. 15-18 mpg towing.
When you're traveling longer distances, that extra 5-8 mpg really adds up. I can go 400+ miles on one tank of diesel, i would be lucky if my gas trucks got 300. Diesels last way longer (and that is a fact), tow better, get better mpg (towing and not towing), have bigger and better components that wont break down after towing for 50k miles. Diesel may be more expensive at the moment but when you're comparing 3.30 to 3.80 your only saving 10 dollars at the pump but your going to go a lot farther with that extra 10 dollars.
Once you OWN and tow with a 3/4 ton you will never go back.
Last thought, you say you are well under the weight limit for a half ton with your boat. the specs given by boat manufactures on "weight" may not include trailer weight, motor weight, and the extremely heavy gear and gas that are in the boat.
Just my 2 cents on the topic. Obviously im giving my opinion to the OP and if you can't afford a 3/4 ton than don't get one, but if you can its well worth it.