Yes, I agree. Perhaps less so in our area than yours (sand v rocks), but still a risk (oysters/random debris) - and a trade-off of sonar capability vs flush/protected. In the end, I decided it was easier to give it a go this way and, if it gets damaged quickly rather than replace I can grind it all back to flat and install an in-hull.
Re: the TM quick-mount, to your point (I think) I'll either need to inset slightly or build-up a little to ensure the mount has a nice, flat surface. I'm leaning towards the latter. Also thinking through location. Dead center minimizes inset/build-up and is aesthetically more pleasing - and fairleads immediately to either side should accommodate anchor rode needs. And I think would allow the TM to operate most efficiently. But offsetting to the port or starboard side of the nose allows a central fairlead, handle, clean spot for a painter - and gets the TM, when stowed, a bit more out of the way and more space for whatever I decide to do for a dodger. My gut tells me to offset - function over form.
I'll be toying with mount/blind options over the next week/10 days before removing the deck and getting on with the work. A cousin has invited my dad and me to join him in S Georgia for a quail hunt mid-month, so that provides a target date for transitioning from planning back to labor.