I agree that there are standards and add that standards are those of craftsmanship. Other than those I am not sure about the artist's intention because as the saying goes "good intentions are not always fulfilled". So I'd say that good intentions are necessary but not sufficient. I think that besides good intentions there has to be readiness at some point in time for the art to be appreciated at least by a favoured few. This is like the claim that art has to some extent to reflect society. At least in its idiom, and rap is without doubt an idiom that is much appreciated. Rap also involves skill although to what degree I cannot say as I am not a musician. The extent to which rap reflect the intents of makers and performers is quite likely to be gauged by whether or not the intent includes commercial intent.
Money as the root of all evil art is not true though. I can think of good artists who did it for their livelihoods. I can even think that popular rap artists do it to earn a crust. I venture to claim that some techniques to render their art popular and commercial also make the art bad art. Those techniques are the use of shock for the sake of the sensation alone and not to enhance any meaning. Perhaps if rap expresses truth it is good art and if it does nothing but seduce listeners into the pleasure of sensation it is bad art. Not that sensationalism is bad per se, but it can be a waste of time and energy that is better expended by learning something good and true.
Standards may be craftsmanship but that is just one aspect of musicianship. Expressiveness and creativity are arguably more important once a functional standard is achieved.
Sure, good intentions surely aren't enough. As a hobby musician whose home recordings are mostly experimental, acid jazz and free jazz I have at times produced some truly rancid, steaming excrement. It may be "art" but I wouldn't call it "good"
Yes, rap does take skill and know-how and it's branching out interestingly. It is, of course, the latest of the waves of musical innovation from poor black Americans - ragtime, blues, jazz, funk and now hop hop. There is a fusion of jazz and hip hop going on, with some nice results. I personally prefer uncommercial music but, yes, some commercial music is amazing.
My father didn't think the music of the 60s and 70s (that I like) was art. He thought it was all crap, in much the same way many of my peers speak of rap and hip hop. Nothing much has changed there.
I agree with you about honest and cynical music, although some cynical music can have its charm. There are performers with all the depth of a Petri dish who simply have a knack for creating viscerally pleasing music. I feel a bit differently to you about sensationalism, though. It's always instructive when artists try different things out. I have more of a beef about formulaic music that the companies deem "safe".