Compared to 7 nights in the Sheraton Tokyo Bay, closer to the Tokyo parks than the Polynesian is and of comparable quality:
7 x $250 room rate = $1750
2 x $1300 flights JFK-NRT = $2600
2 x $150 4-day TDR tickets = $300
Total base trip cost: $4650
Lobbing my support here, but I'll do you one better...
July 1st-July 5th, 2013 (straddling Canada Day and Independence Day): Sheraton Grande Tokyo Bay, 11050yen all in (~$100). 3 Beds, SPG stay and benefits eligible nights - no fancy rates required, booked it via the Sheraton/SPG website. To top it off the parks were very quiet.
It's an "on the monorail" resort by all definitions, the stop is directly across the road (~30 second walk).
I see PLENTY of dates available for ~$143 next year, I'm sure the Hilton and others also have decent rates but people can price shop themselves if seriously interested.
Now when does the math not work quite so well?
-During Japanese Holidays when the parks are slammed and hotel prices easily quadruple.
-Japan is also NOT a seven day resort. There is a reason the maximum days on a park ticket is four.
-Tokyo Bay is not an appropriate place to see Tokyo proper from... I
know lots of people here have done it, but that's just my opinion. Just because you can and the transportation is awesome, doesn't actually mean you should. A second hotel in the city makes way more sense.
-Side Note: My recommendation for HKDL is completely opposite though, get a hotel in the city and don't stay at Disney, just take transit in the one/two days you'd visit.
-If you fall into the theme park fanboi crowd, throw in the cost of a Shinkansen to go down to Universal (and that's realistically a 2+ week vacation you'll be looking at to do both and not completely ignore Japan).
-Realize too that the far superior Universal product right now is Orlando.
It also doesn't work if you visit WDW on a budget, drive in, don't stay on property, etc.
I also would be remiss to oversell it too much. Overseas travel is just not some people's thing, and there is nothing terribly wrong with that. It's a personality/preference thing. I'd always recommend trialling Disneyland resort first, if you don't prefer Disneyland over WDW, Tokyo won't be your thing.
The foreign cuisine, cutesy throwaway merchandise and unknown language would send you running for the hills.