Stagecoach are in a far better position to sort Northampton out than the disgraceful cowboy outfit that is Centrebus.
I travel with Centrebus quite often on MK-Dunstable-Luton route X31. The service is always on time and the vehicles are clean. I had cause to complain to them on one occasion - they responded with multiple written letters, far more than the emails I've had from Stagecoach which avoid the issues and apologise for nothing.
Stagecoach's fares in Northampton are absolutely disgusting. Furthermore seeing as they run most of the town already they've already had and missed their chance to sort it out. Their operation has the feel of knowing they're in charge - fares are over the top, timekeeping is poor and vehicle condition ranges from pretty amazing to absolutely awful.
Compare Stagecoach Northampton with Arriva's recent investments in Milton Keynes - a conscious effort to upsize vehicles, new express routes, new nightbus routes coming down the line, a new information centre, joining the MK business alliances - vehicles are in good nick, timekeeping is so-so and fares are better than SC's fares in Rugby, a town less than half MK's size. So the best thing for Northampton would be Arriva taking First's operation, but they won't because it's not profitable enough for them and Centrebus are someone I'd much rather ride the 28 with than Stagecoach are.