Andy, don't give up on the mixing. I believe it will definitely help you down the road. It will even help you with creativity in how you imagine your songs will sound as well as give you the tools to make it happen.
That being said, I understand what you are feeling because it gets frustrating. Everything I was trying always sounded thin too. One thing I just realized, and please anyone can correct me if I am mistaken, is when I look at the frequency spectrum on the master buss after mixing I see consistency in the wave forms across the whole spectrum. I also learned after trying to EQ on headphones that I constantly made my mixes thinner than they were originally.
I have 2 books about mixing that are good resources that are helping me. They are:
- Mixing Secrets For The Small Studio by Mike Senior (which works with the Mixing Secrets website)
- The Mixing Engineer's Handbook by Bobby Owsinski
Maybe check them out too.
Good luck.