Hi Ian,
I am wondering myself that now that I am autoguiding that a OAG would be a good way to go especially with what you are thinking about like the Qguider or like what I was thinking , a DSI.
With 2-3 sec exposures I can`t see that obtaining a guidestar would be a issue myself and this would like you say eliminate flexure and lighten the load on your mount.
It sounds like a good idea but I dont really know how to implement it with my MPCC and maybe a lumicon OAG...
I would be interested in others experiences in this as well
cheers Gary