The question is what Disney Resort are you comparing to Off-site. Some advantages due to location ( BC Walk to EP, CR walk to MK) and many do offer a uniqure theming experience. I love POR for the gardens and river walkways. WL is beatiful etc.. Many onsite resorts are much nicer than the Marriott Courtyard /Super 8 concrete blocks off I4.
Where the onsite value for me totally diminishes are the values
But honetsly unless you are NOT able to have a car IMO and are totally dependent on buses, I do wonder what is the point seriously of staying at the All Stars.. You get a cheap motel feeling with Zero ( I count 30 min early entrance a joke) benefits besides being in the disney bubble. Pop/AoA do offer some unique experiences, skyliner, some theming. but the rooms itself is nothing special and small.
For me we usually do split between value and Delux. This year we are doing split between PoP and then heading over to Portofino at US. This will most likely be our last year staying at any Disney value hotel. You are looking at 150 at least a night now.. with a great deal.. So let's say average almost 200 a night.. for that I can get a much nicer place off site.
in doing my math.. Staying off-site you need to calculate about 75-90 for rental, park parking fees. For us we rent a car for most days anyways as we like to go shopping, grocery etc.. And some parks we drive to. So by staying on-site we only save the theme park parking. Also many cheap motels/hotels have free parking so that 15 saved can go towards theme park parking.
Back in the day it was actually cheaper staying onsite at the values if you added in DME savings, and lack of rental savings. not anymore.
IF we come back again ( cant believe I wrote that). We will most likely for cost savings. Stay offsite and slum it for 3 nights, rent a car, shop etc.., drop car off, then check into a Delux and used the 100s we saved towards those nights.. Not sure if others think this way, but I would be curious to see of the average on-site guest time decreases vs other years. Expecially with Genie etc.. maybe families decide to spent more for shorter on-site trips and go elsewhere. I loved having a theme park break days, while on-site, to relax, swim and shop. Now IF we come back we need to do experiences in blocks.. so maybe land at MCO , rental to cheap hotel, relax,, shop, Disney Springs, due AK/HS days as those for me are better with a car. and then check in for a couple nights on-site for skyliner and MK/EP.