Nick (or anyone who does so, for that matter) - can you help us understand why you're running more conservative levels at 24-bit?
Like Matt D said, one case is when stealthing and you can't check levels. In that case better to be conservative and boost later. For example, in the case of the V3 w/ 113 dB dynamic range, if you peak at -17dB (really conservative!!) you are still getting 96dB of resolution, equivalent to a DAT recording with the levels perfect and hitting 0.
Another case to be conservative is for recording acoustic/unamplified instruments which can have a huge dynamic range, think drum kits or trumpets close to the source, or perhaps symphony orchestras.
However, in the case of taping rock shows where the mix coming out of the PA is typically highly compressed to begin with, I don't think there is any reason to run your levels significantly more conservatively just because you are rolling at 24 bit. Maybe back off a couple o' dB just to be safe, but in these situations, I would still be shooting to peak at -3dB at least. However, with the increased dynamic range of 24 bit it doesn't hurt too much to be slightly overconservative, if you peak out at -6dB or so you are still pulling a recording with better or comparable resolution to a 16 bit tape with optimal levels.
Peace,
Ben