Only the first two series concern us because they featured a raised roof aft of the C-pillar with slit-windows at its front and sides. These cars featured a third row of seats, so perhaps the raised roof and its fenestration were marketed as amenities for the passengers stuck in back. The third-row seatbacks (and the seats, presumably, though they were placed over the differential) were at the same level as the other seats, so the extra height was probably not necessary for headroom purposes. But the feature might have lessened any claustrophobia for passengers during daylight hours.
The "Vista" label was borrowed from a railcar concept (see here), marketed as Vista-Dome by at least one railroad, the Burlington. So it was a short marketing step from Vista-Dome to Vista-Cruiser for Oldsmobile.
Sales of nearly 60,000 first-series Vista-Cruisers (plus perhaps 25,000 Buick Sport Wagons) were enough to justify continuing the concept when Oldsmobiles and Buicks were redesigned for the 1968 model year.
Although there was nothing really wrong with the Vista-Cruiser concept, there was little that was right about it either, so far as I am concerned. It was basically a fairly small market niche that General Motors could afford to fill in those days.
As for styling, the raised roof added bulk to the overall design of the car and unbalanced it somewhat.
This links the car to the 1964-65 New York World's Fair, where General Motors had a pavilion.
The style appeared again when Oldsmobiles were given redesigned bodies.
The final version.