I think the beaches on Ambergris Caye are just right for strolling. How much beach does one person need?
I don't understand what you mean when you ask for 'a nice beach." Are you talking about the quality of the sand or the square footage? The island is mostly sand - how much is manicured beach depends on how close the facility is built to the water line.
Any resort where you would stay cleans their beaches everyday.
I also don't understand why people don't want to swim over eel grass - it is full of interesting critters.
I think everything is relative - from the pictures I've seen of the beaches in Europe people are elbow to elbow on a big beach.
I grew up in Oregon - if you could see anyone else on the beach you were too close. Some of Oregon's beaches are more than a mile from road to water with sand dunes you can't see over. Northern California, on the other hand, you are lucky if there is any sand between the cliffs and the ocean. Of course both of them have bone chilling water that only kids and crazy adults get in more than knee deep.
The water here is always warm enough, sometimes warmer than the air.

Harriette
Take only pictures leave only bubbles