Saying "I don't know" is a perfectly valid scientific response. But how does one know that something is unknowable ? And then to presume that once something is declared unknowable it is then "irrelevant"? I think that shows at the very least, a lack of imagination.
Every great scientific discovery came about when someone looked at something unusual/out of the ordinary/unreasonable and asked himself "Is there a good reason here why I should consider this abberration important?"
Einstein looked at the material world and noted that we live in three dimensions - but the revolutionary thought came about when he began to think about time - up until then a complete abstract - and recast it in terms of a fourth dimension. Instead of saying that it was unknowable, he continued to dream about it and let the idea evolve until he found a mathmatic key - and sure enough, all four dimensions suddenly worked together beautifully and made all sorts of other equations possible - changing physics as we knew it forever.
What if God/spirituality were a fifth dimension that we just have not been able to find the key to yet? To just shrug and say it's unknowable and therefore irrelevant strikes me as terribly limited and sad. If it were even possible that someone created the cosmos and is responsible for it - and furthermore, is knowable and available for a relationship with us - it strikes me as the single most urgently important idea to pursue while we are alive.
From a negative standpoint, spirituality is relevant just on the basis that many wars are fought over religion and we are affected every single day materially by it. From a positive standpoint, billions of people in the world depend on faith in God to guide them, to comfort them, to sustain them - these are people we all have to interact with all the time. How could that be irrelevant?