Bruce,
for me, one of the great things that I've discovered about fretless is that you can alter intervals minutely to sound more 'in tune', even if it takes them off the lines. I saw Alain Caron talking about this before I got a fretless and couldn't believe that you could hear it, but now i've got one and it's my main voice, I'm more aware of doing it.
Equal temperament is a convenient way of not having to own 12 highly modified basses, and to my ears sounds fine. What sounds 'more fine' is having the ability to alter certain intervals to make them work better.
I think it's a worthwhile persuit to seek to play music that is as expressive as you can - I've experimented with quarter tones and such like, but have yet to find anything in my own playing that grabs me enough to make me devote serious time to it. I'll continue to try to find ways of knowing music better, having more options open to me, one of which is correcting intervals away from equal temperament.
Experiment with it and see what you come up with...
cheers
Steve
http://www.steve-lawson.co.uk