Well, Miss Manners says absolutely not-- the wedding gift should be what the guest can afford. If the hosts need the gifts to help make up for the cost of their wedding, she says, that means the wedding is too expensive.
I agree with her. Otherwise I couldn't have invited friends and family who were on public assistance and/ or starving young students and/ or a little short of cash. We wanted ALL our family and friends there who could come, regardless of income.