Don't understand why one would want to shoot into 3/4inch plywood, but whether they break or not depends on a lot of stuff, the weight of the bow, the arrow shaft spine and weight, whether the arrow was flying straight when it hit, etc. With no point and a large flat surface up front, if the arrow is shot out of a fairly light bow, say 50# or less, it's likely to bounce back rather than break regardless of whether it's compressed or not.
On the other hand, glancing shots, such as those that are likely to occur on 3-D targets, are often likely to break the shaft. And, I agree, given the time and effort that goes into selecting the right shafts and making wood arrows, it does hurt when I break one. I'm willing to pay that price to shoot wood though.