Hah! I don't mean to laugh, but I was out only 4 ours ago on a rocky beach and as I switched out my 75 f 1.8 for my 35mm f2 v 4, and placed the rectangular cap in my teeth, and then my right hand. I got quickly distracted by some scene so the cap never went into my front pocket.
As my son and I were leaving I realized I'd dropped it. We searched the small area about 10 mins. That rocky surface was perfect camouflage for the cap to show itself. We were finally giving up and my son spotted it
I seem to recall that the Asph version of that lens will work on v4 but it looks to be $129.w hood at B&H. I was asking myself the same question you are, would I bother to replace it? And my next thought after recovering it was..."Leave that cap in the closet; use a filter with the hood and be good with it."