I will be the advocate for the other side! Yes...there are a wealth of reasons to immerse yourself in the "Disney Bubble" but an equal number to staying offsite. We have been renting homes (Condo, townhouse, 4/5 bedroom houses) almost annually since 2005. We have never regretted our choice nor had an unhappy experience.
In 2008, we had 10 people, including 4 generations (ages 3 - 89) and rented a 5 bedroom/5 bathroom house. We paid an unbelievable $149/night for the whole place, which included its own pool and spa, in a gorgeous gated resort just minutes from WDW. The resort facilities included a big pool, water slide, clubhouse, playgrounds, and sports courts, as well as 24 hr security on the gate. Obviously we will never see that price again, but we have a beautiful 4 bedroom place lined up for this fall at $139/night. Stayed there 2 years ago and absolutely loved the house.
Besides plenty of beds and bathrooms, we had something most hotels don't provide...private common areas. We could lounge on our own lanai, sit around the kitchen, living or dining rooms. No perching on a bed in your room while you waited. The children loved to get in the pool while we put breakfast together each day. Funny thing is that all us women couldn't wait to get away from our kitchens, but cooking together while able to see and talk to everyone was so much fun that we really ate out very little. We even cooked and ate a Christmas dinner before heading to MCMCP.
It was a huge step-saver, too. We walked out our door, hopped in our vehicles, drove where we wanted and returned at the end of the day and walked straight into our house. No treks through immense properties or down long hallways. This was a real winner whe carrying sleeping children!
We were able to pack very light, because we had our washer and dryer. We'd toss in a load before bed at night, and another before we left for the day. We even came home with clean clothes and room for souvenirs.
In the evenings, we could be as social or solitary as we wanted. Watch tv in your own room, enjoy a drink on the lanai, or soak in the spa, all while the kids were tugged snugly in their beds. You just can't leave 3 yr olds asleep in a hotel room while parents head to a resort pool for a late swim!
We also all agreed that our time away from the intense stimulation of WDW didn't hurt at all. In fact, i really think it was calming for both extremes of our age ranges.
After that experience, we were sold, and every time we go back, we hold the debate. Off site or onsite? We got spoiled. Even last fall when there was just my DD and me there, we were so much happier in our offsite condo, with our own bedrooms and bathrooms, at considerably less than the best value-priced resort we could find.
Oh, rental homes usually come with all the child-related equipment you need, inc strollers and many have games rooms, computers, video games and more. They are just amazing, and come in the widest range of pieces you could imagine. If 3 or 4 families pool what they would spend for sufficient resort rooms, you would be blown away by what is available. Keeping to a budget is a big priority for us and we think we are amazing value going this route, even adding rental car and parking costs.