Old (30 years) school thermal breaks are solid polymide or polyurethane. New thermal breaks are baffled and made from nylon which has less thermal transfer than polymide and PU.Please elaborate and explain what old school thermal breaks are and why they aren't effective? Do you mean to state that a thicker thermal break is less conductive than a thinner one?
I assume there are diminishing returns, at a certain point the thermal break U-value is same as the panel. The main thing I think we want is to make sure our corner extrusions and connectors are not colder than the dew point inside the enclosure.
Yes, U value for the corner needs to be the same as the wall. This would prevent moisture from collecting in places that are hard or can't be (mold) accessed.