The king of Glam, for me at least, is T.Rex.
Most of their big glam songs are in E and use very simple groovy rhythms for the verses with minimal chord changes, then swing into a C-Am-F-G on the choruses, pretty back stuff. It's all very rockabilly/girl group styled 50's "changes."
an example would be "Children of the Revolution" by T.Rex. Here's a Youtube version with crazy nice piano.
For his ballads he often just rocks out the C-Am-F-G the whole time...which of course sounds epic on piano.
Bowie, of course, is more tricky... but alot of his best tracks are also super simple boogie/blues based riffs with insane lyrics.
Glam is more about taking basic rock, kicking up the rhythm and attitude, imho.