I like the idea of spell focus items in D&D5E, but just using them to substitute a material components pouch seems a little lackluster.
Consider this; the term focus, to me, seems to suggest an intensification. As such, why not apply a +1 to your Spell Attack Bonus and your Spell Save DC should your spellcaster elect to use one? The catch, as written in the rules, (If I remember correctly ...) is that you can't cast spells without your Spell Focus.
What do you think? Is it fair House Rule material?