I think it depends on what you consider to be a multiverse. Does it only refer to a rigid structure like the modern 52-universe DC multiverse, or does it include more fluid concepts like Hypertime or Michael Moorcock’s body of work?
I think as fans we tend to overanalyze and categorize things, and the industry is essentially run by fans these days. So there are people out there for whom it matters that Young Justice takes place on “Earth-16” and not simply in the Young Justice continuity. And fans overwhelmingly rejected Hypertime, which was designed not to impose a structure on the DC Multiverse but to describe how it actually works.
I do think there’s value in, as you say, being able to open the door between worlds. One of the oldest tropes of the super-hero story is the crossover. Whether it’s Superman and Batman teaming up, or two versions of the Flash, or Batman and Captain America, it’s a trope with tons of story potential.
If you have a chance, I’d recommend the trade paperback “Planetary: Crossing Worlds” by Warren Ellis. It includes a Batman story in which the team ends up jumping through the multiverse, meeting different variations on Batman (including both the Adam West and Frank Miller versions).