A thinner strike plate seems like an easy thing to try, like Bear Heart said. How do you happen to be using a 1/8" closed foam strike plate anyway, did your bow come that way?
If you're still getting too-stiff action on your bare shafts, maybe you should try a weaker shaft.
As for broadheads, my favorite is the Wensel Woodsman 150 grain screw-in broadhead, which I think comes in the same weight in a glue-on broadhead. If you shoot 145 grain target points, it works out about right because you end up sharpening off about 5 grains from the broadhead. Most people also trim a little off the sharp point and make it into more of a pyramid point.