When game first released, the weapon "economy" was kinda fucked, so you couldn't easily upgrade weapons without dedicating hella hours to the Chalice Dungeons. But when I picked the game back when DLC dropped, I found they had done tons of things to improve player experience, including making it easy to purchase upgrade mats from both vendors in the dream.

And related to that, don't be conservative about spending Insight. There are some cool things that happen based on your insight value, but you get it with ease, so hit up the Insight vendor as you please.