Can I delete the /Developer-3.2.6 or /Developer-3.2.5 folders?
Nuke it (you've got a backup, right?)

If you run sudo /Developer-3.2.6/Library/uninstall-devtools it should clean up things like terminal add ons, but they take little space.

Since you only use gcc and such for homebrew - you'll not need all the SDK and such from this old alternate install of Xcode. One compiler set is plenty unless you're really into maintaining some old code that breaks when the newer compiler sees it.

It's probably from an old install where you could pick an alternate destination - not something Xcode 4 moved around.