Of those listed. only prdoom and vgba are in extras. if you're not working on the other apps yourself and testing your new versions of them. or testing and rating someone else's packages in extras-testing while keeping a backup of your n900 and having flasher-3.5 ready for when it goes wrong, you probably shouldn't have extras-devel or extras-testing enabled at all.

As for extras proper, I agree it shouldn't have broken stuff or stuff that's dangerous.