Business needs must already be changing, it has gone down from 4 course places for BPN to just 2 within the last month.
Picc isn't the best depot to drive at really with all them Hadfields.
Going back to previous experience on preserved lines. If you mean having a go on one of those 1 day courses that cost a fortune, that won't help you much if at all. If your a regular driver on the line then that would help more than just "a bit". Afterall what better experience can you possibly mention in an interview for Driver than experience of driving trains?
The only downside of driving on a pres line is it isn't evidence that you can work on your own, as going off what I've seen, the driver is always with at least 2 other volunteers in the driving cab, along with another 2 or 3 in the back cab! But on the plus side its experience with proper trains rather than Busses on rails.