Steve's right...you can't polish an anodised part without stripping the anodising off first. Some people have used oven cleaner to strip the anodising but you have to be very careful. Oven cleaner will also eat the aluminium if left on too long.
I had my valance trim and header panel trim stripped and polished over the summer. The parts looked very good when I sent them off. When I got them back, they looked awful. There were pits everywhere. The anodising hid those pits very well. I'm going to have to get replacements.
This is just my opinion but if your building a nice driver, you can probably get away with stripping and polishing your existing trim. If your building a show car, then I'd buy the new trim from BE&A. I have his tail panel trim and it looks very nice. It is shinier than stock but that's fine for me. If your building an OE car, then price is of no concern and you'll have to find NOS.