I think blank cards are a great idea! It would take item cards for me from the realm of "neat but it won't work for my campaign" to "what a great product! I'll buy 5 copies!".
I think the blank cards should be non-glossy on both sides, and sold in decks, and yes they should be inexpensive. The only other option I could see is doubling the size of the boosters and making 50% of the cards blank.
Nothing on the front, nothing on the back, generic border, and away we go!