The theory behind AO shaders is pretty simple, the mathematical implementation shouldnt be a problem for a programmer who can program HDRI solutions. So in that respect, it should be possible to put it in bryce.

However, it's defenitely NOT 20-50 times faster allround. It might be very much faster on a simple object, but the more detail u have in your scene or the more data, the more you will see rendertimes increase and you might want to increase the quality too for complex geometry, which boosts rendertimes even more.

AO can be usefull yes, i do use it myself, it's easy to give extra definition to shapes, it's good for faking some natural lighting effects, but it's not always the best solution per se.
AO is a render solution that calculates the amount of occlusion of a point of an object by other surfaces of the object itself and surrounding objects relative to a hemisphere around the scene. This creates a totally uniform occlusion effect that doesn't account for different propperties of different surfaces in terms of light interaction and it ignores actual scene lighting in it's entirety, including color bleeding, caustics, refractions, 'diffuse light bouncing'. By lack of this, naturally, you dont aquire a lighting solution that will always fit all your needs.
In the dark bedroom example for instance you might want a bright streak of light comming from behind curtains, or a slightly opened door, and you will notice AO won't make the light from the bright streak bounce off surfaces and you'll lose the nice soft glow of it that would in real life be cast onto surrounding objects. Shadowing onto surfaces around the a white ceiling would in real life be less intense then on surfaces surrounded by dark objects, AO doesnt do this for you either.

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