I only recently was able to pick up a good set of Lee GND resin filters in the 4x6 format. My 9 stop filter is a Hoya screw on style and is glass. Glass seems to be harder to keep clean and free of scratches. I do know the cheaper plastic style filters I don't care for because they always give an unnatural purple or magenta like hue in the darker areas of the filter. Please keep in mind I am fairly new to using GND filters. I use to tonemap a bunch of things but have learned some things recently with the GND's that will be putting those days behind me a bit more. Always be some situations HDR will still be needed though. :)
I'm in the same boat. I have a few resin filters but have only started to learn how to use them. The others I own are all screw types and only get a work out once in a while. I usually add everything in post. I should try harder to get it right in camera first!
Haha!! I have a rule about post work and whether to do it or not....if I come across a shot that catches my eye and I like it...what else matters? I actually enjoy the actual post work sometimes. Lately I have been making an effort to learn more about filtering and as you said...getting it right in camera. But...I see we are artist. Its our job to represent the scene in front of us however we see it in our own minds. No different than traditional arts. So just keep right on doing what makes you happy because it is working my friend!