Raising the Quality settings in Bryce can get expensive time wise.
Lighting, reflection, HDRI / IBL, Heavy texture mats, Heavy Object content, can all play rolls in a lengthy render. Keep your end result in mind and work it from that angle. If your entire scene is rather simple and you want a super quality, then by all means experiment with setting the bar higher. On the other hand when you've created a complex scene, you can rely on details in the scene to compensate for super fine(clean) renders.

Lots of variables like post work and multi-layered renderings(multiple renders layered together in IE: Photoshop)

I usually test my renders using smaller resolutions, then increase the size for the workable piece. Then composite and postwork in Photoshop.....Other people do not care for post work.

All personal preference & Lots of practice.
Have fun
ICM

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Ockham's razor- It's that simple