"The Church" is a very generalised label. In the UK there are many different denominations of Chritianity, each with its own "dress code" A few wear flamboyant robes frequently, some have beautiful embroidered vestments for special occasions, some wear sombre black or clerical grey, quite a lot wear "geneva bands" with ordinary clothes, to identify them , and some can't be distinguished at all by their clothing. Plus there are congregations of other faiths, with a similar mixture of sartorial tradition. Just as in other walks of life!
The choice of clothing has nothing to do with the genuineness of their calling, and the garments themselves last an extremely long time - they are not exposed to the soup-stains and rips and tears of everyday life - so they are being renewed every few months out of the donations in the collection box.
Have you checked on how much churches are doing for the poor and the despairing, BTW? I think you'll find it passes the cost of those outfits each year by several times. Live and let live.