Hi,
WX_GTK is compiled and installed per the guide on your site, so I'm pretty certain it's not that.
I decided to try the latest stable aMule (2.0.0rc5). It's now been running for almost 5 hours and is showing none of the previous symptoms. The CPU usage has stayed constant (and very low) all the time it's been running. So I'm going to assume it's all fixed. Again :)
Thanks again to everyone who helped. And to everyone else with this problem: upgrading should fix it :)
Aypok...