If it's just that the finish is getting a bit duller and losing its sheen, the best product I have tried by a country mile is AutoGlym Bumper Care and Trim Gel (green label). It's leaves my pillars with an even sheen that lasts for weeks and survives regular washes and rain fall. As they're black, they can probably be revived a lot more easily than the brown, but it might be worth a go as a temp measure.
I also use the gel on the rubber everywhere else - the handbrake and gear lever gaitors have never looked so good! You can forget Autoglym Vinyl & Rubber Care. It's brilliant on the dash and interior, but for exterior and hard wearing areas, this stuff is the business! Michael