A compromise approach I'm considering is
* keeping the current timestamp-with-timezone field type,
* making a stored procedure localEventTime() which converts the
timestamp to source-local-time
* replacing all the occurences in the various apps that point to
event_time with localEventTime()
I'm not thrilled by this because I'm afraid (a) I'll still have to
review every dang query by hand to make sure it makes sense, and (b)
someone sometime will forget to use the stored procedure.