The issue here is whether an alloy track bar is more or less resilient than a steel track bar. Alloy bars aren't like alloy frames (i.e., the stiffest of the bunch and least comfortable). Steel bars are pretty nasty if you're riding on rough surfaces. When I race on a rough track I used to switch to alloy bars just to ease the pounding in a hard race. Of course, now I just do carbon track bars, which is the perfect blend of all desirable traits.