I use to mix on headphones in my younger, novice days....never gave it a second thought, it seemed like what's the dif...???
Then when I moved up to monitors, I realized the dif...but I also went cheap on the monitors...which like most home rec newbs do mainly because of low budgets. It's funny how when you don't have cash to spend, you convince yourself the cheapest alternatives are good enough, and I certainly did that.
Then when I finally decided to get serious about my studio...I dropped the serious cash, and I certainly saw a lot of improvement, and the more I worked with the gear, I could hear better results. I think the stuff I've been working on the last year or so is without a dounbt the best I've ever done...and I'm talking about the audio quality.
Anyway...I'm certainly not in some "great room"...it's just a space that became my studio...with some basic acoustic treatment, and the application of things I've learned.
I find now that getting a decent mix going is no longer an involved process...the gear is all working together as it should, and it all comes down to what goes in during tracking...not what I can manipulate during mixing.
I mean...if you can play commercial music on a set of speakers in your recording space...and it sounds real good, as it should...then you should be able to get decent mixes in the same space.