I think that if you oil all the spokes now, and move each nipple a bit, they will be much less likely to end up seized. Maybe once a year oil all the nipples, loosen each one 1/2 to 1 turn and tighten it again. Then true the wheel. I assume they seize because (a) whatever lubricant was on the spoke thread has evaporated, and (b) the nipple hasn't been moved in years.