Thoughts, suggestions? Is it worth the $350 and extra hassle of moving mid-trip with a family of 7 to stay on-site part of our trip?
I read you r follow up - that you booked an onsite room already, and will save $. I'll still attempt to address this question a bit. In large part, the answer will be subjective. Either way there are pros and cons.
If I were in your shoes, I'd probably keep the rental car for the duration. for me, it would be worth the PoM, especially with a large family. I've been to WDW many times in small and large groups, and with a larger group, having a car comes in handy. In a pinch, taking the car to get around can mean the difference between being on time for dinner or being late. Since you are also swapping hotels, you will also be able to leave part of your luggage in the car.
I've done many split stays. when we change hotels, we put the clean clothes in one bag, and the laundry in another. Then the bag with the laundry stays in the car. We use like a 13-gallon trash bag as a hamper, and that makes it easy to shove the laundry in a suitcase. Just a regular bag can be squashed down easily. It doesn't have to be a space bag to partly act like a space bag, just don't completely knot it off.
In some cases, getting to the parks from an offsite location can be faster than using WDW transportation. In other cases, staying onsite is faster/easier. the timing of the WDW transportation is variable. Part of the value is how much you like driving over not-driving, and how much you like waiting on transportation over having control (driving).
And the other intangible is how much you are excited to be staying onsite. Or how much you like the offsite location/features. Some folks love being able to do laundry, others hate it. Some love to prep their own food, others hate it. We often do split stays because the change of scenery is nice. And then of course, there's the pandemic to consider right now as another wild variable. One trick to split stays, I find, is not to unpack too much. (not putting stuff in drawers. We just open the suitcase, lay it out that way, and take an outfit to wear each day. Laundry goes in a bag.
OH- one BIG factor in moving- it is very easy to leave behind a charging cable. On check out day- as soon as you unplug your electronics (last morning)- pack the cable. they are tiny and back, easy to forget, and a pain to lose mid-trip.