No, they cannot be combined.
We prefer TiW, if you know you will spend the $500 necessary to come out ahead of the $100 purchase price and that you don't already eat at locations that carry a 10% DVC discount (meaning you need to spend even more to over come the 20% discount being closer to 10% at those locations that have a DVC discount as well).
Anyway, don't overthink it - if you spend a good chunck of change in table service restaurants (including on alcohol) - it's a great deal. Free valet parking at the resorts with a TiW card and dining receipt.