Belying the name somewhat, I believe U+3000 is specifically meant for use with Sinoform logographs, having the size of a (fullwidth character) cell, and so it makes little sense in other contexts.
But...the vertical dimensions don't scale so well, at least in my browser. It causes a slight downward shift.
From what I recall, the size of a typical interword space is ⅓ of an em, and traditionally a bit more than this is inserted between sentences (but less than ⅔ of an em). The period itself introduces a fair amount of negative space, and only a skosh more is needed if any.