Realistically looking abstract art is IMHO most useful.

Subject can be real or not (2 options) and painting can be realistic or not (2 options). That gives us 4 possible combinations:

Real subject painted realistically - just use photographs, they are better.

Real subject painted unrealistically, most modern art, as useful as blurry photos of UFOs or yeti.

Unreal subject painted unrealistically. This is most useless, painter have novel vision or idea but is not good enough to convey it, in gamedev they call them "idea guy".

And finally, unreal things painted realistically. Painter have novel vision or idea, and is skilled enough that you can see his vision, this is the only valuable art. And that's what Salvador Dali was.