Upgrading depends on your personal experience. I recently sold an over 10 year old gaming laptop to someone on craigslist who felt it was perfect for him. He wasn't playing any modern games, just doing work. So does your laptop work for what you do with it?
Adding memory will only help if you are periodically maxing out. Older games and software might be OK with 8GB but having 16GB would allow you to have more things running at once without risking maxing out. Actually, if you have a spinning drive you might feel more speed increase from switching to an SSD than adding memory.
As for selling it, it's unlikely you'd get a lot for such an old machine. You should check Ebay to see what similar spec & era machines are going for.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…