For us, we made the step up on a trip where we had
Free Dining. We knew we'd want to upgrade to the regular plan and not just the QSDP that came with the value resorts. Having 4 Disney "adults", once we upgraded the dining plan, it was less than $200 total for us to upgrade for our week-long stay. And that's been it ever since.
Not that we wouldn't stay at a Value if it meant another trip! But once the kids get to be teenagers, that bit of extra space in the room, the extra sink, the bigger beds do all make a difference and allow a more comfortable stay. And we're not hang out at the resorts people either!
But I do have to say even though we don't spend a lot of time at the resort, the amount we do is much more relaxed, more mellow at the moderate resort than we ever felt at the values. We've stayed at Pop, AS Movies, AS Sports, POFQ, and visited POR. Just strolling around the resort, visiting the food court, the pool, coming off the bus, etc.--the vibe is much more relaxed. And for us, it's nice to have that little bit of downtime after the hustle and bustle of the parks. Let's face it--the parks are 100% stimulation 100% of the time! I enjoy not having that at the resort as well.
But again, we wouldn't turn down a stay at a value!