Speaking of exotic languages, I'm somewhat intrigued by Rebol and Red. How bad of an idea is investing any time into learning either of these?
Depends on what you want to do with it. If you're looking to develop mobile or desktop applications it's almost useless. The desktop GUI is stuck in the 80s and as far as I know even that isn't an option for mobile.
If you're doing web apps, it's probably worth a try provided you don't mind writing your own libraries for a lot of stuff.
I believe REBOL and Red shouldn't be confused. The Red project seems to be going on quite lively, with the most recent commit some 9 days ago at the time I'm writing this (see https://github.com/red/red ). That said, it's still not fully complete, but it does most certainly have more modern goals than REBOL -- see e.g. the Roadmap Status page (http://www.red-lang.org/p/roadmap.html) for information about Android bridge (currently reported "90% complete", look for it at the bottom of the page).