IMO, the ticket designations in the past had a lot to do with operational costs. Not just the "coolness" of the ride experience. DL charged more for rides that were expensive to build or expensive to operate. This is why things like the Monorail and the Pack Mules were E-tickets. On the other side, you had something like Adventures thru Inner Space which had Monsanto footing the bill, so even though it was similar in operationally to the HM, they didn't have to charge an E-ticket price.
If Disney were still using the ticket book system, I have no doubt that Soarin' would be an E-ticket, due to the operational costs associated with the ride system. However, they don't use ticket books anymore, so any future "Is this an E-ticket?" questions are going to revolve around the "coolness" factor.
My own personal classification of attractions:
E: These are the attractions that are always ambitious (for the time they were built), enjoyable and impressive. Just being fun isn't enough, just being ambitious isn't enough, just looking or sounding impressive isn't enough.
D: These are the attractions that are usually enjoyable but not always ambitious or impressive. I consider RnRC to be a D ticket. It's a fun coaster, but I don't think the ride is as ambitious or impressive as it needs to be to bump it up to an E-ticket. Ditto for Screamin'.
C: Attractions that tend to be enjoyable and sometimes impressive but not very ambitious.
B: Similar to C, but a notch below in those 3 categories.
A: Things that can be classified as attractions, but are more about providing atmosphere for the surrounding area.
I consider Soarin' a D. I enjoy the sensation of the ride, but the film is on the blah side. The pre-ride buildup, or lack thereof really hurts the attraction, IMO.
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