I went a couple of years ago on a whirlwind tour of Panama. It's hard to compare to Ambergris Caye other than the fact they are both islands.
The things I liked about Bocas (and I'm speaking of Isla Colon) better than Ambergris Caye were: lower food and hotel costs; a little less touristy atmosphere, paved roads, rolling hills and lush scenery, with surfing beaches.
There were three main things that I liked less about Bocas:
1. That the real estate prices were very high considering the state of development it was in.
2. It wasn't as convenient to get to (you just about had to stay in Panama City the first night when you arrived from the States).
3. No real beaches on the town front (it was just all right up to the water). You couldn't go for long walks on the beach like you could on A.C.
I stayed at Hotel Angela which (two Decembers ago), cost me $70 a night, breakfast included, with free internet. Clean but spartan accommodations, great host (retired military man from the states), but seemed a bit high considering what I got.
Since I've only been coming to A.C. for four years, I don't know, but I'd guess that Bocas has some similarities to an earlier time on Isla Bonita--that's what drew me to check it out. For me, the real estate scene (which is to a large degree how I look at a place) was very frustrating. As I said, prices were surprisingly high, even for off-water lots. Also, a lot of the land on the island is not titled but is right of possession (ROP), which, while cheaper, I'd be scared to touch as a gringo.
I took some pics a while back when I started my blog (I'm not advertising, b/c I don't make money--it's just a labor of love), and here's a link: http://investtheworld.blogspot.com/2005_12_01_archive.html
. Unfortunately, I was just learning how to blog, so my day-by-day rantings are basically in reverse order, and my pictures are not of high quality. But hopefully it'll help some.