I have spent a ton. Any time I get an upgrade as soon as raiding/etc. (even questing while leveling) are done I go back and gem, reforge, transmog. I love the transmog feature as I love a lot of the older sets (some of which I was never able to get in vanilla/TBC) so they have some value to me.
I also wish they would allow weapons to be transmogged by 1h/2h. By that I mean if I get a 2h axe but want to use my 2h sword I can (like hunters can transmog guns into bows). Definitely not 1h becoming 2h or anything like that though.