The most important thing you are paying for is location location location at deluxe resorts, and really, that's about it.
There are some other differences for sure, interior vs exterior hallways and different theming for the most part. But those are very much choices of preference. There are some who prefer exterior hallways, ourselves included, and some who prefer interior. Likewise the theming/décor, ambience etc of the resorts are not "better" per se. in Deluxe resorts, simply different. We would prefer the theming of CSR or POR over GF any day. Although the lobby of GF is quite impressive, the rooms and grounds just don't do it for us. Its really all about taste and preference when it comes to that stuff.
The "Value" is another difficult question to answer, ....
I have read people talk about how the Monorail resorts are the best because of ... the monorail. And yet, there are entire threads on these boards dedicated to how terrible the monorail is, how unreliable, slow, broken, etc.
There are also threads on these boards dedicated to how TERRIBLE the bus service from "X" resort is ... but we have never had any real problems with the busses.
For us, the transit just isn't an issue, if you are at a monorail resort, you still have to deal with monorail issues, and still have to take busses (we do all the parks equally). If you are at a "walk in" resort ie: CR, GF, BC, YC, BWI, you are still going to have to take transit to the other parks.
Taking a bus 20-40 mins a day, is more then worth it to save hundreds, or thousands of dollars, especially when even staying deluxe is still going to involve SOME travel time.
Do what works for you, but if staying Mod would mean a longer stay, or another stay, or being able to do something else with the saved money, I'd say stay Mod, I think you vacation experience will be the same, but you will have more cash