> The D5100 sensor is 6016 x 3264, >while D3200 is 6016 x 4000. The D3200 has an approximately >22% advantage in both the vertical and horizontal.
This is probably a typo. The D5100 sensor is 4928 x 3264.
But back to the original question. I have both the D5100 and D3200. While I like both I think the D5100 is more useful with the articulating LCD. I don't think the resolution difference is a big deal as both can produce stunning photos. If I were to buy a used body I would prefer to get a Nikon refurbished body from Adorama or KEH. You would be assured of getting a good working unit along with the strap, manual and software in addition to only the battery and charger you get with a used body from KEH.