If you buy a resale you can buy a different use year. However, if you buy a resale use year that is the same as your present Disney purchased use year, then point and contract administration gets much easier. Disney can make your new contract part of the same base contract and member number. You have one set of banking / borrowing deadlines to remember. It is very easy for Member Services to work with you making reservations within the seven month window at other than your home resort.
As an example, I have three contracts, all with October use year, all with one member number, and with the contract numbers as
contract number .000 = Boardwalk
contract number .001 = Vero
contract number .002 = Hilton Head
All things being relatively equal, I'd go for the same use year. If you can save a bundle of $, then I'd live with the added administrative hassle of different use years.