Whether you use gas or another type of grill, the inside of the lid will likely have buildup from the previous year. Not only does it look gross, it also can be a fire hazard. Use a strong brush, possibly the same kind you use to clean the grill grates, or maybe a nylon brush, depending on the grill material. Personally, I don't care about scratches inside the lid of my grill — I'm just happy when it's clean.
A paint scraper is also handy for cleaning out built-up gunk.