You can indeed clear coat aluminum, but I'd have a tough time figuring out what would be gained from doing so.
One potential option would be to have the plate clear anodized, which would harden up the brushed swirls, but it potentially would change the color of the material significantly.
If you do spray a clear lacquer over the plate, you could change the gloss level (good) and potentially protect from scratches (maybe not that useful), but at some point that coating may begin to flake off, and that can be really frustrating.
The best option for a clear coat, IMO, would be to have the plate powder coated. This will go on thicker and adhere better than other products you could get at your local home improvement store (and you can have the transformer covers coated at the same time).
-PB