I'm not sure I can see Southend being that much of a goldmine in itself. Its catchment isn't any greater than a number of other destinations that don't exactly have great service from Dublin.
What they do have though is the only flight from Southend that will connect you onto long-haul. And with no transatlantic from Stansted, with Heathrow and Gatwick a decent distance away, that could mean the yields are very good on Southend-originating pax. However, I don't see that meaning exceptionally large numbers that would justify transfering the route to an A319/320.