I've been meaning to post some sort of answer to your question but it still mostly defeats me: where the problem lies I mean.
There is a sort of spiritual cross-over which I have never quite understood.
During my first year studying music I had a conversion experience after some years of semi-atheism (I had been quite involved earlier in my life, including confirmation and Christian union). After this experience I completely lost my ability to 'play'. I could still manage the notes but they no longer meant anything. Music had been an instinctive language to me and suddenly I no longer understood it. It was a scary and bewildering experience: for years it had been the mainstay of my life: I wanted to be a professional musician. Now I longed to throw it all in and it was actually my chaplain (a catholic monk and priest) who persuaded me not to and to complete my training willy-nilly. Gradually, out of sheer necessity, I had to relearn all my musical 'sense' from the bottom up and when I moved abroad and was surrounded by people who were really enthusiastic about music (I taught the subject) I learned to love it again albeit in a different kind of way . . . . Ever since then my spiritual life has criss-crossed back and forth. At rare times the two strands (prayer and music) have lived side by side, but if one goes into the ascendency then the other wanes as though the two strands were sitting on a seesaw . . . but, as I say, balance has been rare.
The period following my conviction (I had pictures on my puter, and that period in my life is an important part of this whole picture also) was such a time. Music became an absolute necessity: after years of crippling self-doubt I composed avidly and copiously for about four years before the self-doubt [and my prayer] began again to take the ascendency and yet the psalms were always my inspiration. My music is, to me at least, the psalms in sound.
With poetry, the barrier has been more cut and dried. When I read a poem, however good it is,(I love Manley-Hopkins and Dylan Thomas for their sheer playful musicality, and because they tend not to take themselves too seriously - which is a very important point I think.) I do struggle so with the concept of 'art for art's sake'. [I know it's rather iconoclastic to talk like this, but it is a gut feeling.]
I dont think it is any coincidence that my main conversion experience happened a few minutes after I attended midday office at a monastery for the very first time. This was the monastery where my chaplain was a monk (this man changed my life in so many ways.) We were visiting for the day. They sang the psalms of course. I had come across the psalms before in the Anglican version and found them fairly puzzling. Hymns also did nothing for me: moralistic and often manipulative; frequently sentimental in a rather sickly way, often with hideous nationalistic overtones. But those psalms (in the 'grail' version): they were quite different. They werent being 'nice' about God. They werent being 'moralistic', they werent trying to teach me anything (although some do I know) they were much more basic than that, and they werent trying to be 'art' either. They were dark, at times 'ugly' even (although in a translucent kind of way), but they were all, even the 'ugly' ones, addressed to God, or related to God, or reflecting God, or expressing God. He was always there: at bad times as well as good. Not always loved: often feared, even disliked or apparently cruel, but always there nevertheless, especially when He wasn't(and He is often absent in the psalms). This was poetry in three dimensions instead of two and when the 'third dimension' was missing then that's what the psalm was about.
Please dont think that I am suggesting that poetry is not a 'wonderful thing'. What I have learnt to accept is that my view of art is changed beyond all recognition by my sense of the centrality of God - not just in a 'sunday' way, or even just a 'daily' way and I struggle with art which does not recognise this. This isnt to say that God has to be 'mentioned'. He doesnt - and certainly not in a sentimental or 'hymny' way. In fact, I prefer Him not to be, come to think of it.
It's a complicated picture, as I said.
Musically the problem becomes even more complex. The modern concept of purely instrumental music starts really with the period of Bach and Vivaldi, both of whom I suppose could be said to balance on that rare apex between 'religious' and 'secular' which I was trying to describe above. But when we get to Mozart and Beethoven (both of whom I have loved) the picture is gradually altered. It has to do with prayer somehow, but its difficult for me to say anything more coherent about it than that. Maybe I will understand it better later. . . . . this is getting too long, but perhaps you can see why!
I think that 'art for art's sake' is an important part of human life, its just that I cannot locate - for the moment at least - where that more playful part of my own spiritual life resides . . . . although the word 'playful' might be a clue worth following up . . . . .