perhaps scaling back the number of spells to a single new spell from any list would be more appropriate?
I initially based this invocation on the Bard's Magical Secrets ability. I still think the power level of this invocation is fair, but perhaps scaling back the number of spells to a single new spell from any list would be more appropriate? Also, I like the suggestion from @Hemlock, but I don't think I would limit it to only Wizards or Sorcerer spell lists. I think I would go for Bard, Cleric, Druid, Sorcerer, Warlock, and Wizard spell lists. This way, it gives quite a bit of flexibility, but still remains within the realm of spells meant for a 5th level character.
1. Allow ranged weapons for Pact of Blade. Yes, I know ranged combat is sweet, but I love the idea of a spectral archer. Would probably put a limit on the number of arrows summoned, if any. Since this is just for my home game, I am not worried, because my players are not always looking for the best mechanical option, just whatever helps their characters tear concept most.
Here's another invocation I've been considering.
Damning Hex
Prerequisite: 5th level, Hex spell
Your aptitude with using the Hex spell has grown to the point that it requires minimal effort. When you cast the Hex spell, you no longer require concentration to maintain the spell.
That... is probably not something I would allow at my table. It turns Hex into a bit too much of a must-have. I'm pretty happy with the existing Hex/warlock relationship, wherein Hex is a fun and useful thing to do sometimes with your concentration in low-intensity combat because of its low action-economy cost and effect on ability checks (e.g. Athletics)--but not a part of baseline damage.
Additionally, it is already on par with the invocation Sign of Ill Omen. By the time you are using 5th level spell slots, Bestow Curse no longer requires concentration, and Hex has a 24 hour duration. Bestow Curse will be a one time use spell, sure, but it is also much more menacing for the encounter, whereas Hex could already potentially go on all day long. This just takes the need to constantly roll concentration checks to maintain it.