Seriously though, maybe the best tweak is exercise?

Yes, yes, and YES. To put a label onto why exercise improves enjoyment, I can't say but it is a thing I've experienced over and over again.

Another thing that always work for me is coffee. Raises my alert level and I bet this also improves my hearing in a way or two. 

I also believe a good ear-cleaning regimen goes a long way. Something very few of us have and Q-tip is NOT the answer.

Don't forget sleep! Big influence on mood which affects your listening enjoyment. I unsure about actual hearing though. Thanks for the encouragement to get more cardio, maybe that will help my ringing.

This is one of BEST tweaks in audio listening I have ever experienced in addition to gear cleaning, air purification, moisture removals, ear cleaning and so on.  It cures my ear TINNITUS (at least a few hours after my morning 5-10K run) and my mind is sooooooo ready for a long-day listening on weekends.  This is a wonderful no cost tweak in the history of my audio listening, ever.  Good for your health as a side benefit too.

PS - I've also found that a good ear cleaning regimen helps a lot.  If I don't take care of my ear was my speakers will start to skew left.

The solution I've found is a good body wash and lots of lather and water.  So long as I do that regularly I don't need to resort to more.