Would not save a dime. You need to understand how MS and its reservation system is funded. MS and its reservation system have four sources of funding: (a) a $1 per member annual charge referred to as the
DVC Reservation Component in the annual budget; (b) all the breakage income (rental income that the applicable Disney entities get from renting rooms still open at 60 days out) that exceeds the amount that offsets dues; the total breakage income that offsets dues is that amount which equals 2.5% of the annual operations budget excluding certain items in the budget; breakage income has always exceeded that amount; (c) the fees charged for trading out to non-DVC resorts; and (d) the annual management fee paid to DVC which is always 12.5% of the annual dues budget excluding certain items (such as the management fee, taxes, and some others).
That is it. Source (a) is a fixed amount of dues and thus cannot vary due to use of MS services. Sources (b) and (c) consist of money that is outside of anything covered by dues. Source (d) is a set percentage of the total budget that may vary in amount annually but not percentage and thus if none or all of it is used for MS reservation services, the amount of dues paid for the management fee remains the same.
Thus, your dues will not vary according to the amount actually paid for MS services and the reservation system. What can vary is the amount Disney gets to keep from that management fee and breakage income that is not spent on MS services and the reservation system. In other words, based on the sources of income to pay for MS and the reservation system, the less Disney spends on MS and the reservation system the more money it gets to keep from breakage income and the management fee.