I ran into this exact problem before with my Samsung LED tv and an IR emitter that had a really tiny dab of Super Glue on it to hold it in position since it seemed that no amount of the supplied replacement double-stick tape adhesive would hold. I tried to buff things clean and shiny on the plastic but to no avail whatsoever. Some things make it look a bit better, but you will always see it.
If you want it perfect, I would skip the Bondo, MDF frame, etc. Quite simply, I would mask off everything but the front facing part of the frame, do a very light scuff sand, then prime with plastic-grade primer and top with three to five coats of a high-gloss spray paint. You will obviously have to mask off any IR sensor if it is contained in the face frame. It will be perfect again in no time, provided you do a quality spray paint job with multiple light coats. Just my two cents.