I think actually being able to drive one -- P5, not P4 -- is important. Handling, noise levels, acceleration, all those very physical things -- to me (and to many) are really important, whether it's a $6,000 car or a $60,000 car. The prototype can't provide answers to any of those questions. Maybe some form of Oculus Rift display one could try? But I'd rather drive one in person.
If Elio keeps being smart, they're going to keep ownership of a number of early vehicles just so people -- reservation holder in particular -- CAN get a physical experience of the car before buying.
A lot depends on how many will accept the reported experience of others. It will take the Real P5 and other models, but that's enough for a sizeable population of reservationists it seems.