The company has a track record of operating older aircraft. In general, they are quite reliable, although the 757s have had their teething problems. When the 737s were added to the fleet, they also had their share of teething problems. During the summer, there were only a few times a 737 went tech causing problems to the schedules.
As for new aircraft, well I think there will never be any 'new' aircraft, like Ryanair or Ezy. Rumours around about some NGs arriving, but I don't believe it, as they are just too expensive, and we don't like spending money.
I would expect a few bargain older aircraft to be bought in the next couple of years, as these are parked up in the desert, either 737 or 757s.