My view is that EasyJet really are sqeezing everything they can out of Southend. Further closure of popular routes from Stansted like Barcelona in January 2013 and it seems now Alicante as well from June 2013 will not be because they are underperforming, there is certainly demand and huge potential for big profits for those routes from Stansted. The only explanation is that they are doing it to take the strain off Southend. I think also it's absolutely the case that Southend is only as successful as it is due to prices being considerably lower than other London airports in alot of cases, but I think it is articially low and it won't stay that way for ever. Also flying times are more attractive on the Southend routes with the ideal 10am departures to the Med as opposed to the choice of leaving at 6am or getting there at 10pm on Stansted flights. EasyJet are not stupid, they know everything that the typical customer desires and have effectively made sure that Southend flights are the perfect scenario whilst there are drawbacks with the others (like higher fares), but are perservered with due to the benefits of flying to a larger airport like Gatwick or Stansted (eg. better flight connections or quicker travelling time to London etc.) They will struggle to maintain this approach for ever.
In addition, BAA will sell Stansted not too far in the future and will in theory become much more competitive than it currently is, and shouldn't take too long to do that being seperatley owned from Heathrow. What if the new owners promissed lower landing fees or attracted EasyJet in some other way, which being more competitive, which is almost a certainty, could be quite easily achieved. It could really make Southend suffer. I bet if we never had this reccession then EasyJet would have never used Southend. In the longer term, when the economy recovers, Southend is always going to struggle with the feirce competition of the much larger, well connected (not BAA owned) Stansted.