sonoma9600, check the search feature on this site for “oblique hit” and you will find a few other answers on this subject from me. Especially read my reply to “Ray286”.
Your longest iron has the most flexible shaft; your shortest iron has the stiffest shaft. This is how all shafts install as we shorten them. Control from the short irons is the most important thing and therefore they have “stiffer” shafts. When you walk into a store or pro shop and pick up a “sold separately” wedge from almost any manufacture it has a stiff shaft in it. I certainly do not want a soft shaft in my wedge for any reason and especially chipping or pitching the ball. First of all, there is no advantage to this and what if I want to hit a full shot with it? Simply by design, the wedges have so much loft that you do not compress the ball nearly as much as with the less lofted clubs. This makes hitting a wedge near or exactly on face center less important. So, as irons get longer in club length and lesser in loft and we swing them faster, we need shafts to have more flex and a resulting increase in torque to give us some help in getting the ball airborne and feel better. Try hitting an 18 degree loft #1 iron with an X-300 Dynamic Gold shaft. Any miss hit will cause your gold fillings to fall out (not to mention a significant loss in distance hit) and every face center shot will feel like you hit it with a board.
From your post, I want to make it clear that I am not advocating stiffer shafts in wedges than what you would normally play. You should play the flex that fits you. The stiffer shaft part in your same flex just happens as I explained above through shaft trimming (shorter lengths). However, in almost all cases, you will not hurt your game by playing with a stiffer shaft in your wedges from buying a separate wedge to put in your bag. My over all preference is to play the same shaft and flex in your wedges as your set, but remember that wedges are heavier than all the other clubs in the set, so they will make the same flex shaft feel more flexible and also play more flexible. Just look at a frequency curve when plotting the entire set including the wedges.
Finally, the Rifle spinner wedge shaft is a good shaft and has nothing wrong with it. It is used by a few (very few) pros on tour for the exact reason you posted. In my opinion 98 % of all golfers including our better playing amateur golfers will not benefit from this shaft over a normal wedge shaft. It is also priced quite high for a steel shaft at around $18.00 each. I personally am not ready to pay this much for any steel shaft.
