Hey Tom, whether it'll be a new shaft on your old club head, or a new set of clubs all together, they both fall into a club fitting properties, and that's where you're going to boil things down to if you want to get the best from either method you go with. If you chose to reshaft your clubs, find a place where they are willing to work with you on fitting you with the correct shaft before it's installed on all irons. It will probably take more work to match the flex and weights that are correct for you- but it can be done. On the other hand, you can also do the same with a new set of AP2 and be fitted entirely for loft/lie/length/flex..etc. with your current measures, strength and skills paired with the newer technology yielding to your best possible performances. So get fitted for it either way.

In any case, here is a link for a good read:
www.pga.com/.../golf-club-fitting-qa-professional-golf-club-fitter