Imagine developing with the ultimate 10x setup: several files, documentation, and debuggers open at once, with a zen nature background. Or making music, or painting, or even writing a research paper.
Imagine playing a video game but the environment wraps around you. Imagine watching movies in a virtual theater with a simulated 100-inch TV (one of Apple's demos). Even reading and browsing the web can be improved with an ambient environment and extra space for more stuff.
Is it worth $3500? For end-users probably not, but if it genuinely makes professionals and hobbyists substantially more productive, it will be worth $3500 or even way more. How much money would you spend to write, code, create faster?
Of course, this assumes the VR actually performs, and whether a bigger screen and immersion actually makes people work faster. As of now it seems VR is still a gimmick which impresses people at first, but doesn't provide much outside of niche experiences; which, if this holds for the Vision Pro, makes it very much not worth the price.