Hmm, I have the exact experience, visual mode in UDB is SUPER useful, you just have to realize it's NOT for building in, just editing. But once you have your sectors placed, you can do a lot of things: raising & lowering sectors, including 3D floor, copy and placing things, visually changing the slopes of floors, adjusting lighting, changing textures. There's probably a few more things, but I spend a lot of time in it because it's indispensible for visualizing how everything looks, while letting you change a lot as well.
I think what's confusing for new users is that once you're in visual mode, pretty much everything besides selecting walls and flats and raising or lowering sector heights requires a keybind (though pressing the button to get into visual mode also gets you out of it). That and a lot of the tools do need a bit of explaining to fully understand them-but really, that's true for any super powerful software. No one expects to open up Maya or 3DSMax and be able to know how to use everything in it-you have to watch tutorials to learn, or at the very least read the reference manual.