It's worth noting that our planet was formed by "meteorite" impacts and that our own moon is the (geologically important) result of Mars smacking into our planet, but let's focus on impacts after, say, the Archaen.
If we lived on the moon, impact craters would pretty important to our geology. As it is, it's perhaps a lot more important to our biology than to our geology, though strictly by association. For one thing, every meteorite that has ever hit an ocean basin (almost %75 of the earth's surface) has been plowed into a subduction zone; that includes monsters over 100km in diameter. As for those whose erosional remnants can be found on continents, finding them isn't easy and interpreting their formation isn't without controversy. In fact, finding many of them is a matter of walking back specific meteorite-related minerals to a likely source and focusing there.
As for diamonds, their occurrence in impacts is rare and, economic importance, rarer still. From Charlie Murphy's paper, Economic Mineral Deposits in Impact Structures: A Review
Diamonds generally occur in very small amounts in impact melt rocks. Grieve and Masaitis (1994) estimated an average concentration of about 10 ppb.
As for economically important placer occurrences of industrial-grade diamonds, their source is still controversial. Geochemistry may prove a kimberlite source for these diamonds....just like those in South Africa.
A little bit of lunar scenery, here on earth.
