The problem:
When I get to the mid-late game in most CRPG's, I'm spending more time juggling inventory than progressing the story, because there are so many crafting recipes and ingredients used for many different things. It's normally only a few end products I'm actually interested in, but due to the complexity of the crafting chains, I normally end up making spreadsheets to help me remember which ingredients I can safely sell from my own inventory, and which I should remember to buy from merchants. For me, it detracts significantly from my enjoyment of the game that I have to cross-reference information manually. And yes, I could just ignore the crafting aspect, but in most games that would handicap me with regards to available equipment, and I'm OCD enough that I can't really let it go either.
The proposed solution:
Allow players to mark recipes of interest, and then highlight all related ingredients in your own inventory and in merchant inventories, preferably through all links of the crafting chain. That way, marking junk items in your own inventory becomes a lot easier, and spotting relevant items in merchant inventories becomes easier. Actually, you should be able to mark any item as relevant, such as a thingy you suspect will be important later on, but which you don't have a recipe for yet.
The next level would be a shopping assistant, which could look at merchant inventories and suggest a shopping list based on your marked recipes, to show that you could buy the last pieces needed to make item X. Maybe even a tickmark in the shopping list to show that you want to craft this item immediately after purchase, so you don't have to go through all the steps yourself, especially if it's a three-link crafting chain.
This could also be expanded to non-crafting items, such that you could mark that you'd like a staff that gave a bonus to Aerotheurge, for example, and any such items would also be highlighted in the vendor inventory.
