I, personally, have had good luck with refinishing my plastic lenses and I have 103k+ miles on my car. It is a time consuming process, but worth it IMO. I used a mild rubbing compound then polishing compound and finished with a plastic polish (made by 3M or similar company). Like I said, it took a while, but my time is free to me

. You can even add a wet sanding step (or several) to this process depending on the condition of the lenses.
If you choose the HID assembly, the light quality benefits are obvious. I have not researched what is involved (wiring, etc. wise) with the conversion. Another option is replacing the stock lamps with a higher lamp temperature bulb such as Sylvania SilverStar bulbs. Keep in mind they do not have the same lamp life as stock bulbs due to the higher temp. They are around $30.00 per set. If you choose this route, I recommend using lamp socket lube which helps with lamp life. I have found that I do not even have to use the high beams because of the increased visibility with these bulbs.
Hope that helps a bit. Good luck.