Thanks to all who replied, especially to Klaus for his thoughts.

Here's the UPDATE:
Well we decided to have the evaporator done since it was long overdue. We just brought the car home and everything seemed very good. The dash was tight and no squeaks, rattles, or scratches. All electronics (lights, stereo, glovebox CD changer, etc) seems to work fine. I checked the A/C lines from the firewall to the accumulator and nothing seemed to have been replaced -- they are all the original ones. It was an expensive repair. My wife and I were a little hesitant at first but everything worked fine. We now have that 'new car' scent coming through the vents. ;-)

The shop showed me the old evaporator with dye covering almost a fourth of it. He said that he blew compressed air in it and observed that it was leaking bad. He explained that originally (with leaking evaporator and rotted accumulator) the pressure in the A/C system was low. When they vacated the system, installed a new accumulator, and then filled the system with refrigerant, the greater pressure caused the leaking evaporator to give up sooner.
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Brian M. - 1998 S70GLT, 1998 S70 GTA