Great minds think alike Cazzy. I am just about to do the same thing, that silver plastic frame cover is not something I like very much.
I am gunna use a satin black as well, just about any paint nowadays will go over hard plastic, like others are saying, give it a good scuff with a scourer or around 600 to 800 wet or dry sand paper, wipe with prepsol or similar and paint. I just going to do them with a pressure pack, the same paint I have been using on the handlebars I have been respraying a lot lately. Post up some pics if you do it, and so will I.