It really depends on the makeup of your family (primarily how many Disney Adults you have) and what your rack rate is.
Here's roughly how much you save per night with Free Dining for various combinations:
1 Adult: $32 on QSDP, $42 on
DDP
1 Adult, 1 Child: $42 on QSDP, $54 on DDP
1 Adult, 2 Children: $52 on QSDP, $66 on DDP
1 Adult, 3 Children: $62 on QSDP, $78 on DDP
2 Adults: $64 on QSDP, $84 on DDP
2 Adults, 1 Child: $74 on QSDP, $96 on DDP
2 Adults, 2 Children: $84 on QSDP, $108 on DDP
2 Adults, 3 Children: $94 on QSDP, $120 on DDP
3 Adults: $96 on QSDP, $126 on DDP
3 Adults, 1 Child: $106 on QSDP, $138 on DDP
3 Adults, 2 Children: $116 on QSDP, $150 on DDP
4 Adults: $128 on QSDP, $168 on DDP
4 Adults, 1 Child: $138 on QSDP, $180 on DDP
5 Adults: $160 on QSDP, $210 on DDP
Here's how much you save per night with a 40% Room discount (assuming 12.5% hotel tax) depending on the rack rate of your room:
Values in Value Season ($82): $37
Values in October ($105): $47
Moderates in Value Season ($149): $67
Moderates in October ($170): $77
AKL & WL in Value Season ($240): $108
Contemporary in Value Season ($285): $128
AKL & WL in Most of October ($300): $135
Contemporary in Most of October ($330): $149
YC, BC, BWI in Value Season ($340): $153
Poly in Value Season ($365): $164
YC, BC, BWI in Most of October ($390): $176
GF in Value Season ($410): $185
Poly in Most of October ($425): $191
GF in Most of October ($465): $209
These are rough numbers that don't include weekend surcharges, other holidays and higher rates, upgraded rooms, suites, etc., but they should give you a good idea.