If you examine the JAA PPL and the NPPL what is the difference? Both are examined to the same standard therefore the candidate needs a similar level of training. The quoted lower hours for a NPPL is a nonsense, it takes what it takes to achieve the standard. The only difference syllabus wise is that the NPPL does not include radio navigation or one exercise on basic IF; both of which are well worth doing from a safety perspective.
With gliding experience there is a saving to be made as the NPPL has better credits than the JAA PPL which at most gives you a 10 hour credit for 100 hours gliding. The medical is also cheaper however; with EASA approaching two things need to be considered.
a) the NPPL will not be valid on EASA aircraft post April 2012
b) the EASA alternative the LAPL is based upon an ICAO medical standard so any savings there may be lost.
The real point is that if you start training for a PPL it will make no difference to the training in the early stages which licence you finally decide to go for. See how it goes and then decide which way to continue by calculating the cost to the licence issue point. By April/May the EASA regulation will be incorporated into EU law and the way forward will be a little clearer. By the time you complete you training the NPPL may not exist.