I'm not sure I would favorably compare a 20-minute walk alongside a canal (and under a major roadway) to a stroll down Main Street USA. The walk to Epcot is a little better due to the resort theming but when you get right down to it, it's still just a walk past a handful of stores and restaurants.
If I were the type to spend 75% of my vacation time hanging out in the World Showcase, then I would probably have a higher opinion of the resort's proximity. As it is, staying at BWV still means that 2/3 of my destinations (MK, AK, DTD, waterparks) are a bus or car ride away. And those 15-20 minute walks can be particularly grueling after spending 6 hours criss-crossing an enormous theme park.
The location of the Grand Californian is truly an on-site perk for
Disneyland. As for the DVC's at WDW--not so much in my opinion. More than half of our WDW stays have been at OKW and SSR, and Bonnet Creek seems similar in many ways. We would lose some on-site perks but none are things that we would struggle to live without: early entry--rarely use it;
DDP purchase--used once; package delivery--never use it; Magical Express--used once.