The idea of taste itself may seem a bit out of step with our times, but lots of valuable things are so that doesn't bother me in the least. Tastes do certainly vary from one person to another and, even more interesting, from one period in a person's life to another. I've just been reading in The Blackwell Guide to Aesthetics (published in 2004 so reasonably up to date) and discovered a useful essay by Ted Cohen on "The Philosophy of Taste: Thoughts on the Idea". I won't recapitulate his discussion, but take it as a springboard for my own.
Just looking at a single person's history of taste, it is perfectly normal for it to change over time. Musically, for example, it is entirely usual for one's taste to change over time, especially if one is undertaking a course of study in music. With exposure to more and more different styles in music, different historical periods and with training in theory and audible recognition (ear-training), one's taste develops. It becomes possible to distinguish different kinds of music just as one might distinguish different varietals of grapes from going to organized wine-tastings. With the ability to distinguish French Baroque music from Italian or the lute fantasias of John Dowland from those of Francesco da Milano might also come the slightly different ability to distinguish greater from lesser quality--to be able to hear the difference between the counterpoint of Bach from that of, say, Telemann.
If one's taste can develop with exposure, training and study, then the only way to make sense of this is to assume something like a 'standard of taste'. One can only understand one's own improved taste over time in terms of being able to better distinguish the elements of a musical composition and comprehend better its structure and expression. To those for whom relativism is an 'absolute truth' this may well be anathema, but relativism exacts an enormous price: not only does it make it impossible to discuss disagreements over taste, it even makes it impossible to understand one's own improvement in taste over time.
I am always looking to improve my own musical taste because I believe there is a direct link between that and my compositional choices. It is of enormous benefit if I can look at something I just wrote and say, "hmm, well, that's not quite good enough..." If I can do that with my own music, then why can't I do that with the music of others? Assuming one has the necessary competence, of course.