Okay- so I will say Maddie still takes naps, so does my older one Olivia sometimes, but both seem to do ok without one if we areout doing something...
So Basically our plan was to get to rope drop everyday tour have lunch go back to the resort for naps/rest/swim and then return to the park that evening and stay til close. Well this didn't happen once our whole trip!! Lol!
Getting the stroller packed and on the bus sucks, and organizing all your bags that you need with small kiddos and then the kiddos themselves is also a feat. By the time we got to the park we didn't want to do it all over again more times than we needed. It also took a while to use the buses and like you said, eats a lot of time.
We ended up just going and going and Maddie would nap in the stroller when she got too tired, or on a dark ride or in a show, lol. She never got too fussy bc she was always entertained and had new things to do and see! I'd say most her frustrations came from wanting to just run around and play more!
My suggestion is just see how it goes. I think you'll know if your kids are all getting cranky that you should just head back and rest. But they may do fine like mine! One suggestion would be to stop late morning and again maybe late afternoon at a playground/run around type area (all the parks have one or more) and just let the kids run around!! They'll be waiting a lot! In lines, for shows, for parades, and then in strollers a lot too...this helps them just burn energy and be free! I think you'll find if you do that most the time your kids will be able to hang in there or just nap on the go. Also try to do some shows or dark rides in the AC when it's heat of the day and most crowded. Look for the least popular attractions like Carousel of Progress at MK or Ellen's Energy Adventure at Epcot! Those are long, cool, nap rides for babies and kids with no wait hardly ever!
If you've planned your trip well then your not going to be one of those families who are having meltdowns and such and your kids are going to be enjoying WDW as much as you (or more) and they might not want to leave either!!
We did open-close all our days except one where we went to DTD and the girls both did fine (15 months and 4yrs at the time) we really had no tears the whole trip except for when Maddie wanted to be free to run around and she had to get back in the stroller or something...
It's good that your preparing for the possibility of returning to your room though, that way you won't be bummed you have to leave the park if that happens! And then if you don't it will just be bonus time!!
Hope that helps some!!