My character has a cape equipped, but its not showing up on him. I see that there are characters wearing capes in the GOG screenshots. Is that only in the expansions, or am I missing something?

Sounds like you are missing something. My character's cape is definitely visible when equipped. Perhaps its something about the particular cape you are using?

Unless you manually disabled capes in the nwnplayer.ini (visible cloaks=0), there's no reason they wouldn't show up. You could try to install the critical rebuild patch, might help as well (just google "hotu critical rebuild 1.69").

Link to the windows version of critical rebuild patch for v 1.69:

http://nwn.bioware.com/support/patch_english_hotu.html

(Skip step 1. Go directly to step 2 - downloading the patch.)

i would try step 1 first, if it works, great!
EDIT: and if it doesn't, then do step 2

It won't work, BioWare doesn't really support the updater anymore, hasn't for a couple of years now.