I'm working on a project right now based on the STM Nucleo board. It has some similarities to the Maple, though it uses the mbed framework. I ultimately need it because it gives me a 32-bit processor at 100 MHz with gobs of flash and RAM (half a meg of flash, 128k of RAM!).

I could have used a Due, but there are reasons I chose not to that are not really relevant for this post (though one simple reason is that a Nucleo is only $10.33).

If you move out of the AVR/PIC world into the more powerful microcontrollers, you'll find that you go up significantly in complexity. Bubbles in pipelines make it hard to predict timings, internal memory buses, etc. While it is true that you can find some clean dev environments for using them, it's a darker, colder place to be in some ways. For example, the STM forums are populated by relatively harsh folk, though they do know a lot about the chips.

That said, it may be worth it for the power, depending on your project. I'm doing multiple ethernet interfaces and trying to get to line speed, so my current project makes it worth it.