I've tried less direct measures of mood - including how much time I spend meditating per day, and how many journal entries I write per day.
These aren't direct measures, and they don't work over the short term. You can't tell anything without a few months of data, but over the space of months and years I've found they have given a very powerful insight into how my mood has changed. There are some obvious features - e.g. when I'm depressed, I don't meditate, so I can see my depressions by looking for these troughs in my data, as well as some longer term patterns that I can relate to changes in my mood.
Over the shorter term I have found that recording something simple once a day can be effective - e.g. "did I feel depressed?", "did I feel disturbed?". This takes a bit of care and subtlety to do right, and if you have a mood disorder or depression it can lead to many days in a row of simply saying "yes". However, this makes the "no" days much more interesting if and when they occur, and even more so if a pattern emerges. I've found it helpful not to expect to learn anything from this for at least a month, and to be ok with boring data.
I think this kind of daily check-in relates to mindfulness - not in the sense of being constantly in the present, but in the sense of directing your attention in a non-evaluative manner to some aspect of yourself and simply observing.
My experience is that repeating this over a period of time - a couple of months or longer, has helped me to develop more intuition about my mood, and also more patience for times when I'm not doing so well - because I can more easily remember that it's not always like that.
I think the music tracking idea is a great one too - and I would imagine that over time you'd see some interesting patterns. I'd suggest that you'll probably find something interesting in the more 'gross' features of the data - e.g. how many times per day you do it at all, what days do you not engage in the practice, as much as you will in the moment by moment tracking.