I've been running my Suzuki Vitara for about 4 years with out a front plate, after it got ripped off in the woods. I get the occasional double take from the roving constabulary, but no one has pulled me over yet.
You can clean it with a pencil eraser if you don't have contact cleaner. Rub it over the contact areas on the circuit board too. Wipe the crud off the eraser with a cloth (your blue jeans work pretty good) as it gets dirty.
Spent 1/2 the day detailing the R to be ready for Kawartha Street Rod Association's 'Street Scene cruise - in' at the Peterborough Zoo. We should be hosting 350 - 400 custom cars and trucks. I'll be parking cars and slicing onions all day. Life is good !