I took a tour in 1988, when I was 15 years old. My mom went to high school with Lisa Fell (Billy Costa's wife and then-GSM at Kiss), so I used the connection to break the ice. I'm sure that much of the building's interior has changed since then, but at the time it was amazing. Even if you only get as far as the lobby, there's a great hand-painted mural on the wall that was put up in the 80s- it's got dozens of faces on it, including some of the biggest superstars of that era as well as the Kiss DJs.
I have a few pictures that I took that day, including shots of the studio (with J.J. Wright and what looks like a half-dozen huge cart racks). I'll try to get them scanned and uploaded somewhere.