Unless we are out of town or away from the boat for an extended period, the engine intake valve is left open. All the others are closed when we are not aboard.
This regimen works for me, and no way would I promote it for others.....
Best advice is always to close 'em all when you are gone.
Also, I have replaced *all* of the 1988 OEM Marelon RC Marine thruhulls with the later ForeSpar model 93 seacocks.
There are no original bilge hoses remaining in the boat -- all have been replaced, some twice.
(As my friend Bob will tell you, after narrowly avoiding sinking, quality hoses, clamps, and thruhulls are a Big Deal.)