Ah, I just posted on the manufacturing page about those vias. For some reason I didn't see a notification of your post and I figured it's a somewhat different topic. I tried to delete the post but it seems that's not possible.
In any case, I look at it from a different way. As you increase the diameter of the hole you increase the 'track width' in a linear way ('track width' = ~6 * radius). However, you also take surface area away and that increases in a quadratic way (lost area = ~3 * radius * radius).
Having said that, you make a good point about soldering, The hole needs to be wide enough so the solder gets wicked through all the way. What is the ideal size for that?
On the negative side you mention the thermal relieves. Why are they even necessary? Can't you just leave everything copper and to avoid for the copper to bleed out you expose the copper (none of that green/blue/purple color coating) right around the via. That assumes solder will try to stay close to the exposed copper and not get into areas where there is 'paint'. Then again, maybe the thermal relieves keep the heat within that small area, i.e. the copper outside the thermal relieve is much cooler, hence the solder does not bleed out.