I'm your classic "weekend warrior" with a white collar day job and for me, my band is my 2nd job. In other words, I try to apply the same standards of performance and professionalism to my gigs as I do Monday-Friday at the office. By the same token, I expect to be fairly compensated on my 2nd job, just as I am at my day job. If I want to play for free, I'll do that at my church. But pretty much any other situation, it needs to be financially worth my while.
+1
<----Same boat as you (without the white collar job). I do have a great day job. And, yes, I do this as a second job (with about 3 bands). I've, thankfully, been "around" enough to learn a few lessons along the way.
Some of those lessons were addressed in my earlier post.
: )

But if the bar is making lots of money from your fans, then they may well overlook deficiencies in these other areas. I mention that because I often hear "That band is lame, how are they getting so many gigs?" The answer may well be, "They have lots of friends who drink".