There is noting wrong in buying a gift for your wife in Ramadhan as long as you are not ostentatious. Wastage is a sin, whether it is done during Ramadhan or outside. Offering gifts to enhance love is a sunnah; there is no reason to condemn it as long as you do not overspend. The Prophet (peace be upon him) is reported to have said, "Exchange gifts, and strengthen your love for one another."