Yeah pretty nice shots here, one thing I would say is you can tell the riders are not in the thick of 'action.' The way they are seated on the bike you can tell they are going slower and also not racing?!?
Croft is a great circuit to shoot at and I definately would say keep going back their to practice, I was stood in the same place as where you were last year and I was really blown away about how close the track is to spectators.