I have worked with Matte Black (not matte clear). If you sand, I don't think you will have any luck matching the Matte finish without respraying. I had a few dirty areas in my Matte black that I needed to fix. I figured I would end up respraying those areas, but I tried to spot sand first and sand or buff my way back to the Matte finish. I could get a somewhat similar sheen, but no where near close enough for what I was doing. I tried several grits of wet sanding, as well as some compounds. I ended up doing a quick sand on the entire panel and shooting another coat. Looks perfect now.
If you decide you can't live with the dirt in there, it wouldn't hurt to try a few things before respraying.