I think the answer to your question is...it depends. I spent 75 and recently 30 more for Horizons. I personally still love playing this game, and have recently found my way back to it after being away for a while (Thanks Rocket League!). Several of us are coming back after being away for a while... Yes, initially you have to grind to get credits, but you know, I don't mind it. I enjoy trade missions and avoiding interdiction. I'm going to try to beef up my Cobra III and then start doing some fighting. As with anything worth doing, you get out of it what you put into it. This game does not spoon-feed you, and that is part of what I love about it!
If you get bored, just try switching things up. There is mining, fighting, planetary landings (with horizons expansion), piracy, bounty hunting, etc... and try to find some buddies to join up with. It makes it better