Should I fix my plasma?

LCDs and Plasmas are generally not worth being repaired -- unless it was a premium Plasma like the Pioneer Kuro. Given it's a Philips Plasma at 50", you can pickup a Samsung Plasma at 51" for approximately $500 which will give you better blacks and a better picture than your legacy philips plasma. Repairing your Plasma will likely cost you at a minimum $350++ So not worth it.

If you have a splattering of dead pixels the only fix would be a replacement panel. If it is even available the cost would probably exceed that of 2 new Panasonic VT50's.
Time for a new TV, 1080p, 3d if you care, digital tuner, lower energy consumpsion, latest technology and all new parts. Fixing a 7 year old TV leaves you with a new part and a bunch of 7 year old parts doomed to fail.
Just my advice.

Agreed. Don't throw good money after bad...

Get a new TV and and upgrade in the process. Get better picture quality, probably lower power consumption and a "reset" of the clock ticking on all of the remaining components in the old TV.

When it comes to flat screen TVs, buy as cheap as you can, consistent with a good picture. I got my Panasonic 42" plasma this year, and will be surprised if it lasts five years. Great viewing experience. $398 at walmart.