Assuming you have a glass face, then it should hold up to the sunlight. But the cells may not.
Anybody know if the typical silicone cells generate significant power in the UV an IR bands? If not, one should probably shield for UV and IR.
Heat dissipation would certainly be an issue with too a concentrated system. I've been looking at the Sanyo Bifacial panels, and they specifically say not to install mirrors to the back face.
The triple junction cells actually are rated to have better efficiency with concentrated power than without. I think they are kind of out of reach from most home users, but I think they are typically sold with a little tiny solar cell and a lens concentrator in front, and a solar tracking system. It is likely the standard silicone cells would also have efficiency improvements with concentrated power (other than the heat issue).
There was a discussion on this BBS a while ago about vertical mounted panels with a piece of stainless mounted horizontally below (with hinges/springs) to act as a mirror. The idea was that it would be easier to maintain, and keep free from ice and snow. Passive with the "tracking".
I don't know if it was ever tested, but the theory sounded good.