But once you multiply all the dice, and factor in the spellpower, it adds up. You're looking at an average of +1 per die per arrow, so +7 once you have all the enhancements (with an additional +2 or the crit, if you go with AA T5 instead of DWS); multiplied by spellpower so, say, +21 even at 200 spellpower which you can get fairly early on in your adventuring career. And then you factor in doubleshot and hitting with 2 or more arrows...
I just went down to play with the dummy, and I'm doing +50 or so more with acid arrows vs. force, with a fairly negligible difference between acid and force spellpowers. With each arrow. It adds up *really* quickly. (And that was just a test run of 10 or so shots with each, before I either got tired of waiting for the dummy to reset, or accidentally killed it.)
Also, as unbongwah said, ghostly does stack with blurry/displacement. It's multiplicative, though, not additive; it effectively provides 8% with blurry (10% of the 80% that blur leaves unconcealed) and 5% with displacement (10% of 50%).