There is no plastic paint that will hold up.  Best thing to do is sand them.  You'll be surprised how well they polish up.  Put some time into it and use different grit sandpaper to get a great polished look.

There are many articles out on the net on doing this process. 

It all depends on how deep your scratches are.  If they are not that deep, start with 600 wet/dry and see how that removes the scratches.  240 wet/dry should only be for really deep scratches as it takes a lot of work to go from 240 up to nice shiny plastic again (2000-3000 wet/dry sand paper).

As your finishing with one grit sand paper, you will move up to the next level until you end up at 2000 or 3000.  Last step, one guy says he has good results with Mothers Plastic Polish with a polishing towel.

All sanding and polishing should be done by hand or low speed power tools.  All sand paper should be automotive wet/dry type (3M seems to be the best/easy to purchase).

So figure, if you start at 240 for rough scratches, you could then use 400/600/800/1000/2000/ then Mothers Polish.

Once you've gone thru this process but some time has passed and your plastic is not as nice looking again, I like using Maxima SC1 Silicon spray.  This stuff rocks!  I use it on my quads and my SxS.

Alternative short cut process - Sand out the rough scratches and get up to using around 400 grit sand paper then use floor polish to put multiple coats onto the plastic.  I've used ZEP Polish before, but it will flake off and has to be reapplied.

In the past, I've also used a heat gun to melt the plastic back to a shine.  Have to be careful as it is very easy to burn the plastic.

Good luck,
Larry