Short answer to your specific question: Not worth it..and you can't do it anyway as you said your speakers are not capable.. There are theoretical benefits and those have nothing to do with clipping that Rich mentioned, and are not significant unless you do "active" biamping. Practically speaking I doubt those benefits would translate into audible improvements but like the claims of Pass Lab, Bounder, McIntosh sounding better than Parasound, Bryston or ATI, it is hard to prove one way or another. You can try it, I have enough amps and speakers to try but too lazy to do so I biwired, that's easy to do. If your speakers don't have provision for biwire then you can't do either biwire or biamp without modifying them. Biwire is not the same as biamp but with a big amp it can come close to "passive" biamping in terms of the theoretical benefits. I heard no difference.
Rich: Your example of bass clipping won't affect the treble sounds good but don't you think the preamp may clip anyway in some of those scenarios?