At the risk of a derail, here's (roughly) what I would do with components, given a clean slate to work from:
- Rebalance all spells to remove the need for expensive components. That may mean some spells need moved up a level.
- All spells now require Verbal, Somatic, and Material components. The Material component can be anything thematically appropriate, either to the spell or to the caster - they're not specified in the book. Players are encouraged, but not required, to provide some description of how they cast the spell, in the same way that casters of martial characters are encouraged but not required to describe how they make their attacks.
- A character using a spell focus can skip using any one of the three components. Most Wizards therefore cast spells with a flick of their wand and a magic word.
- A character can also remove any one of the three components by using an action to "pre-cast" part of the spell. This can be combined with the focus, as above.
- A character can also remove all components by using a slot one level higher, but gains no other benefits of doing so.
- I would then introduce four types of "expensive" material components: Lore, Special Materials, Reagents, and Residuum. These cannot be purchased - they must either be created in downtime or found while adventuring. (I'll get to why there are four different ones later...)
- Casters can optionally use an expensive component when casting a spell (the value consumed depends on the spell level). This allows the spell to be cast as if using a slot one level higher, to a maximum of the highest level slot the caster could normally use. (So a 7th level Wizard could use it to boost a fireball, but not an ice storm. Only one boost is allowed in this manner, and it is always added last.
- But those same four types of components are also used to craft magic items, and Wizards use Lore to learn new spells. (Which is why there are different types, so different items can require different costs. Lore, as the name implies, is secret knowledge. Special Materials are things like meteorite iron, religious icons, or whatever. Reagents are similar but much more organic - unicorn horn, dragon's tears, mistletoe, etc. And Residuum is raw, unprocessed magic.)
- Under this model, a captured spellbook provides a source of Lore that can be repurposed for any use, rather than a textbook allowing you to learn the specific spells therein. (Under this model, a spell is effectively a cheat code for reality, but they're encrypted for the specific caster. So you can't learn a spell directly, you have to learn the techniques to allow you to derive your own cheat code.)
There's more, but that's enough, and the whole thing would need some more fleshing out anyway. So I'll stop there.