I view the Mustang as nice but plain on the inside. And yes I've spent time in there poking around. The radio cluster is boring as all heck, and the guages are...fine.
The only points I can give them over the Camaro, honestly, is the rubberized material they covered half the dash with. It's very nice...but I don't fondle my dashboard while driving, and the Camaro's looks lightyears better without compromising usability, imo...so win = Camaro in my book.