All of my trips since the advent of Prestige Class have been in the off-season (February). Initially there was no restriction on access for passengers in the regular sleeper class, though on my most recent trip, in 2019, the first two rows of seats in the Park car dome had bands saying they were reserved for prestige travelers. Otherwise we had full use of the Park car. VIA has also added a Skyline car ahead of the prestige cars and the diner, and the dome there is open to all sleeper passengers. Plus there's a third dome near the front that's open to coach travelers, though the staff was discouraging us from using that on our last trip.
The remake of the prestige cars, including the Park car, is really impressive, and overall the atmosphere is a bit more festive for everyone. I was afraid some of the prestige folks might be frowning at sharing space with us ordinary mortals, but in fact they were all having a great time, and we shared some good conversations.