People not being able to rely on the service is a far bigger problem than too many taxis, a Taxi using culture has developed in Dublin as users are (were) confident they can (could) get a taxi (for their morning commute or trip to the airport for example) back before deregulation they made sure they were up early enough for the bus or had organised a lift, that's why Taxis in Dublin are probably busier than those in Monaghan despite Monaghan having 3 times as many passengers per Taxi.
Dublin is in Danger of losing it's Taxi using culture if confidence in the service reduces much further.
A few more Taxis probably wouldn't be a bad thing.