I guess the decision for POR vs. Family Suite would be what you value. It's an extra $40 a night.
Consider:
1. The pool at POR has a slide ... will you or the kids be disappointed without one?
2. The kitchenette at ASMu means you could eat some breakfasts there with the micro and bigger fridge ... would you be able to bring some food, use a delivery service, or pick some food up to save you some of that extra money?
3. Is the bed setup -- queen in the bedroom, three beds in the living area -- better or worse for you than two doubles and a trundle? Would having a door between you and your kids allow everyone to sleep better? Do you plan to return to your resort for naps?
4. Would you use the TS restaurant or the boat to DTD at POR?
5. Would your kids enjoy the free poolside activities at ASMU or the activities offered at POR?
Honestly it comes down to whether that extra $400 buys you enough "value" to make it worth staying there. I think that's why anyone pays for any resort -- they value the convenience of a monorail, having queen beds, a nice view, walking distance to Epcot, a kitchen, etc.
PHXscuba