I don't think it's time yet for Assetto Corsa 2. The game doesn't look outdated nor ugly like rFactor 2, for instance, especially now with all the improvements achived by the community. I think it can still hold for another couple of years. Also, as you say, the advantage of it being a bit old and not very hardware demanding means that we can use VR, tripple screens, and even max out the graphic options, and make it look even better while keeping high fps as we go on updating our CPUs or graphic cards.
However, I would like to know about the future plans the developer has as regard this title. I really hope they don't consider ACC the evolution of AC, and forsake our game without any continuation. ACC is what it is: GT3 and online races. AC is much much more than that. It's way more ambitious, with lots of different cars, tracks and ways to enjoy.