I think the whole strength issue is a red herring. The OP did not question the strength of ropes. I can see a whole bunch of people thinking "I'm gonna keep my ropes dry because it'll be stronger" (the same folk who are convinced that P bolts will pull out if they look at them too hard).
Wet or Dry, part wet or part dry, the ropes are plenty strong enough.
I think the issue that should be paramount in the Wet or Dry rope debate is the effect of heat from your racks/stops/bobbins/fig8/HMS krabs (italian hitch)/ID's/GriGri/stitch Plates/ATC's or what ever you preferred descending device.
On Dry ropes, descenders can get incredibly hot, enough to melt the plastic fibres on the sheaf. It trashes rope very quickly, making them stiff and hard to handle. Since the strength is in the core - I'm not sure what effect a scorched sheaf has on the strength of the rope, but I'm willing to bet that since its stiff, the knot will be weaker.
For the reason of scorching of the sheaf, IMHO, SRT ropes should always be wet. Full Stop.
Other than the increase in strength over the (already plenty strong enough) wet rope and the fact that its a bit lighter to carry, can anyone give me an advantage of dry rope that trumps not scorching your ropes with your descender.