Doesn't aggravated trespass require an intent to damage/disrupt? If damage/disruption is caused unintentionally then it can still be trespass?
Aggravated trespass is something slightly different, it’s basically trespass but with the addition that you are trying to stop other people doing something which they have a right to do. Hunt saboteurs attempting to disrupt a pheasant shoot on private land can be charged with aggravated trespass for example.
I guess the point is that as there is no punishment for trespass, then unless you cause damage, and are sued to recover those damages, then from a practical point of view, trespass doesn't really exist as a punishable offence without damage.
If you willfully damage anything during the trespass then you could be charged with criminal damage. In theory a landowner could attempt to sue you for cycling along a footpath even though you don’t perceive any damage – the very act of being there is having an effect on the surroundings, crushing his grass for example, I would suspect (and hope) that he would be laughed out of court though.
Edit: a more likely course of action if you were a habitual trespasser would be that the landowner could apply for an injunction against you, if you disobeyed that then you could be found in contempt of court and in a whole world of trouble, I've never seen a footpath that's that good!.