thanks a lot for the swift and extensive replies. Just to clarify as it is not clear from my original post: The winter here is long and when I can not go sailing I do enjoy the tinkering a lot, too. Thus when thinking about changing parts of the boat the main motivation for me is simply that I enjoy the process of trying to understand something in theory and then implementing it on the boat. The possibility of increased performance is more of a side note - I am fully aware that if I had any of the top guys boats and they were in a Bladerider I would probably not stand a chance around a race course.
Now concerning the topic of a lowered rig in our German moth group Chris Rashley has been quoted to claim an increase of 0.5 knots over a standard rig. That would be more than one boat length every 100m, which I, based on my limited experiences when lining up with others that have the low rig, was finding hard to believe. I am happy that your general opinion seems to be that it is most likely not nearly as significant, especially as I am on the upper end of weight and height compared to the ideal moth sailor:
Currently I still use the high mast stump with a straight boom and have not had too many difficulties to get stuck underneath. Lowering the rig would also mean I have to kink the boom, which inevitably will add some weight, which is also true for modifying the compression bars and thus not helping low wind performance.
This is also a very valid point that had me concerned and will, together with the other points you mentioned, have me stay with my current setup: I do enjoy how resilient the Mach2 has been so far and I really don't want to change that.
Thanks also to Dave Clark and Team_GBR for clarifying some things concerning the endplate effect.
On the Lennon Sails website they have some short text about the A3.5m developed by Dylan, which is described by 'countering the direction of travel on [the other sails]' from which I read that the current trend is definitely not the holy grail yet.