I have a similar dilemma, 2004 with DA that is starting to show it's age. My main issue is the shifters are getting to their end of life, the rest of the bike is awesome.
Having shopped around, and previously gone through the upgrade cycle, I'm pretty sure that the best value is in the new bike.
Its up to you if 105 is acceptable, for my
good bike I'm inclined to go DA, but there is a price for that.
On the upside, if you spring for the DA model you usually get the nice wheels, carbon cockpit, etc...
I like this one.