Most Xpel film ( if not, all of them..if i'm not mistaken) are self-healing. So as long as you maintain it like the rest of the car, it should stay clean and in good condition.
Film can be polished, to some extend, just like paint. On self-healing film, like the Xpel one, I don't believe any extra protection is needed since the film has it own unique feature of self-healing.
Regular film can receive nano-coating or spray wax/sealant.