What would be the balance effects of adding extra Divination spells?

Question

I am playing a Divination wizard at the moment and quite disappointed that there are only 17 Divination spells, so I thought I would look at some homebrew ones to talk to the DM about.

The question is, that assuming I create balanced spells, what are the effects on the power of the Divination sub-class of increasing the total number of Divination spells?

In particular Divination wizards have:

Expert Divination

Beginning at 6th level, casting Divination spells comes so easily to you that it expends only a fraction of your spellcasting efforts. When you cast a Divination spell of 2nd level or higher using a spell slot, you regain one expended spell slot. The slot you regain must be of a level lower than the spell you cast, and can't be of higher level than 5th.

I know that generally this isn't a well thought of power, but I am worried that, particularly if I add combat spells that this can quickly become overpowered.

A good answer will have experience of adding additional homebrew Divination spells into the game, but a well thought out answer which can explain the reasoning (or show some maths) will be equally well received.

For full disclosure, the party that I am with has a War Wizard, Wild Magic Sorcerer, Cleric (Not sure the sub-class) and Rogue. The spells that I am looking at would be combat related, probably one of each level from 4-8, with an additional non-combat spell from 6-8. None of the combat spells would do damage, they would all be defensive or offensive buffs (See this spell as an example, assuming the damage was removed).

Answer 1

It's unclear, but Portent is very powerful

I'm currently playing a Divination Wizard and I've considered this very issue myself. While we can't get into designer intent as to why there aren't as many Divination spells, I can tell you that the Portent feature is incredibly powerful given my experience with it.

It feels like if I were to be able to have that feature AND have more spells available for Expert Divination as a combat buff to reopen used spell slots, the Divination Wizard would be vastly more powerful than it's counterparts.

Looking it at through another lens

While a HUGE focus of D&D is combat, that isn't the whole game. And the Divination spells have a lot of application outside of combat. It may be worth talking to your DM (I know I will) about creating encounters/situations that make those spells more useful so that you get the Expert Divination effects from them.

The problem is in your spell availability as well. As you only 'naturally' get two new spells per level, it's hard to use that scant resource growth on rarely used spells. I don't know what your spell scroll availability is in your world, but that is another thing to discuss with your DM to help you build a useful combat wizard, but also have your Divination spells and Expert Divination a useful tool for non-combat encounters.