It's not going to be worth anything more as it is a bit scuffed up, missing stuff, etc. Maybe a little more but even if you flip it for $150 you made $75 whole dollars. There was a time these were worth a ton because this and the DP deluxe were your only good Vader helmet options.
You could probably sell it for a bit more as mentioned but just a few pizzas worth.
This is actually a very, very nice helmet. A lot of the old Classic Actions are pretty beat up. My advice is to fix it up, new grills, tusks, paint job, etc. and then just keep it and enjoy. It's a nice base helmet you got cheap. Once you put all the work into it you will want to charge more than most will pay as there are so many option out there now. Quasimodo being the best and Darth Ugly being a great cheaper alternative.
Rather than trying to make a few hundred bucks off a lot of hard work, just fix it and enjoy it. Believe me, I have had to, and still may need to do it and although I can make good money off a prop when all is said and done I don't think I am even making minimum wage.
Re-furbish and enjoy.
Tom
It is a very nice base helmet.