I've never stayed at a Deluxe, so I don't know what I'm missing, I suppose. In fact, I've only stayed on property once before, at CBR. I was considering trying a deluxe this time, and had even had it all priced out, could afford it, etc. But then, I did the math on a moderate, and realized that the $1000Cdn extra I wouldn't be spending on the room could be spent not counting the cost of anything else we wanted to do. I've had that luxury once before (it was in Cancun on our honeymoon

), and to me, that's worth more than a few extra square feet and a private balcony
We loved CBR, especially the pool and the hot tub, and didn't feel we were missing out on anything. And we're looking forward to POFQ this time.
That said, I suppose if anyone asked the question whether it was necessary to stay in a moderate, or would value do, I suppose my minimum requirement (a hottub) would become apparent. So I suppose it depends on what your minimum requirement is. If it's a balcony, or indoor access to your room, than a deluxe would be necessary. But, if all the amenities you need are available in a moderate, that's probably the way to go. And then go and do an Epcot tour, or have dinner at V&A's, or something else extravagant.
Ciao,
Mort.