The 17-55 and 24-105 both feature 3 stop image stabilisation, so you certainly won't lose out from that angle if you make that switch. The 24-70/4 however has a 4 stop hybrid IS system. Hybrid is only of any real use at near macro focusing distances, but the extra stop will make a difference at normal focusing distances.
The 17-55 on crop is the equivalent of a 27-88/4.5 IS on full frame - so the 24-105 (when mounted on full frame) is wider, longer, and vaguely better at gathering light (together with a correspondingly narrower DoF). Not to mention other gains such as weather sealing and build quality.
From what I can tell from the reviews, the 24-70/4 is no sharper than the 24-105, and actually has a more distracting bokeh. I'd only consider the 24-70/4 over it if you really don't need the reach, but you do need the macro capability - and are willing to pay for it.
However, for 24-70/4 money you could buy a 24-105 and a 100 (non L) macro.