I didn't see Experience, MaxExperience as returns for
Inspect.Unit.Detail, but either the wiki needs updating or the API is missing the info. Once a player hits level 50, then MaxExperience is 500 000 per planar level. It is levels 1-49 that are missing.
I am working on Broker Bar, which will have the ability to display such plugins; I'd provide a link, but the addon is far from functional.
I want this plugin as well, so stay tuned to the official forums, RiftUI, and Curse.