nope, there's no reason to. nema17's are plenty strong to drive the machine and their small size is one of the ways we managed to create a machine that will fit on your desktop.
switching to nema23's would drastically reduce your build volume, and make the XY stage much heavier. you'd have to re-design the XY carriage as well.
basically, its not a simple plug-and-play, it would be possible, but why?
we do sell nema23 motors in the online store if you simply want nema23's. =)