For reference: There is a duell in the module where a shaman tries to secretly help one NPC by continously casting Cure Wounds on him while supposedly only helping him "stand up" after he intentionally let‘s himself fall prone. To spot this, a PC has to specifically declare checking for interventions a then suceed a DC 15 perception-check despite being within earshot…
your first paragraph is literally the book rules for spell components. You either have a focus/components pouch for mundane components and anything with a gold amount needs to be spent to cast.
Very few spells actually have a costly material component for it to ever come up anyway.
Can't hide somatic or verbal components without being a Sorcerer for the meta magic though. Otherwise you're literally undermining one of the key features of that class.
Spell components exist literally for the reason stated at the end: so the DM can keep in check the power of the spellcaster as needed for the scenario by limiting what spells are available to be cast.