Routing the water hoses like that would be a nice clean setup, I like it. The thing is, like George mentioned, (hot) coolant will only flow through the manifold when the heater is turned on. I reckon that would be ok though: The reasopn for heating the manifold is to help keeping the fuel atomised/evaporated. With 'normal' temps the manifold gets heated enough (by far imo) by the exhaust manifold. So there wont be any problem not running the water hoses through it.
I also have the weber carb, and did not connect these hoses: never had any problems so far. Maybe when temps are below or getting close to freezing it might be neccesary to pump some extra heat into the intake manifold, but you would also be using the heater when its freezing right? (I would...)
I was actually thinking of putting a heat shield in between the exhaust and intake manifold to keep the manifold even cooler (or better: less hot) then it is in my current setup. In other words: I wouldn't even bother connecting the plumbing.

Cheers, Ben
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)