On the classic ships, I do not think there is any significant difference whatsoever between the two bedrooms versus Royal suites. We stayed in the Roy on the Wonder and took a peek into the two bedroom on the last morning. Truly a minimal difference (mostly just style issues). On the new ships, there is a quantum leap from the one bedroom to the Royal. We stayed in the Walt last year on the Dream and, again, checked out a one bedroom on the last morning. A huge difference in size and interior amenities. Do not get me wrong, I would be fine in a one bedroom on the new ships, however, the Royals do offer more of an "over the top" experience. I did do a review of the Walt on the Dream on this website (can use the search function with something like "Walt Disney suite dream" to find it). Certainly there is a point of diminishing benefits for the costs involved in the Royal on the new ships, however, the two bedrooms as well as Royals on the classic ships are priced much more competitively.
DWF