Would it be balanced to allow the darkvision spell to target multiple creatures when cast with higher-level spell slots?

Question

The Darkvision spell, by default, can target only one creature and gains no benefit from upcasting (= using a spell slot higher than the spell's level).

You touch a willing creature to grant it the ability to see in the dark. For the duration, that creature has darkvision out to a range of 60 feet.

Since my level 7 moon druid has two party members without darkvision, I asked my DM if he could allow me to cast darkvision at higher levels to target additional creatures; more precisely, one additional target for each spell slot level above 2nd (similar to spells like Charm Person or Hold Person).
For example, if cast at 3rd level, I can target two creatures, while casting it at 5th level would allow me to target 4 creatures, and so on.

Anyways, he did choose to allow it, and I've used it a number of times so far. However, since allowing this spell to be upcast is so intuitive - I was really surprised when I found out it wasn't possible by RAW - I can't help but wondering if there are any balancing issues to allowing the upcasting of the spell.

To be clear, I'm not asking why the designers didn't allow upcasting the spell, though the answer to my question might easily overlap with the designers' reasons.
What I want to know is whether or not any balancing issues exist that should prevent me / my DM (I also DM occasionally) from houseruling that it is possible to upcast the spell.

Answer 1

Darkvision is a very situational ability, so the issues caused by having this ability will probably depend on how important darkness is.

It's exceptionally easy to end up with a party where every member has darkvision (both of my current groups are in this boat!), unless the DM places some restriction on darkvision-having races. Because it's available to so many races by default, and because it requires a spell slot, this is perfectly balanced. If anything, it may be unbalanced against you, as it takes up spell slots.

It could easily be very powerful in a campaign like Out of the Abyss, if most of the party didn't have darkvision, but that's a unique campaign with a literally very dark setting.

Of the races available in the PHB, 6 of the 9 have darkvision as a sense. This is something that is easily available to the majority of players from level one, and therefore, is exceptionally unlikely to create an unbalanced situation.

Answer 2

I tried this once

For what it's worth, I allowed this around the time this question was asked although I did not see the question itself until this week.

The party had five characters with racial darkvision (grey elf sorcerer, wood elf ranger, mountain dwarf druid, half-orc barbarian, half-elf wizard) and three without (human monk, human fighter, human paladin). The L6 druid caster had the darkvision spell and I allowed him to upcast it to affect one additional creature for each level.

The party was light on AoE spells (fireball from the wizard; moonbeam and lightning bolt from the (Circle of the Mountain) druid; slow from the sorcerer). In practice, it meant that the druid had to make the decision of casting darkvision as a utility spell for easier and more stealthy exploration at the cost of having fewer lightning bolts. Since the particular scenario (Expedition to the Barrier Peaks) included plenty of both exploration and combat, I found it an interesting tradeoff and a balanced upcast option.

More detail can be found in the Campaign Log I maintain; the Barrier Peaks entries run from posts 157-214.

Answer 3

I find it best to think about balancing questions by putting the alternatives side-by-side and asking "Is one clearly superior to the other - that is, would I always choose this over that?" If the answer is "yes" then its unbalanced.

The follow up question is more subtle - "Are there situations where I would always choose option A and situations where I would always choose option B and rarely or never situations where I would choose neither?" If the answer is "yes" then the solution may be unbalanced because it turns a sometimes useful ability into an always useful ability. It is not necessarily unbalanced because there may be limitations that prevent abuse. For example, spell slots fall into the category of always being useful but they are limited by number of uses.

So, lets see how your options stack up:

1. Use 2 2nd level spell slots (out of 3 total at 7th level), or
2. Use 1 3rd level spell slot (out of 3 total at 7th level).

To me this is a no brainier - I would always use the 3rd level slot. Therefore, its unbalanced.

However, if instead of 1 person per higher level slot you had 1 person for every 2 slots higher the calculation becomes:

1. Use 2 2nd level spell slots (out of 3 total at 7th level), or
2. Use 1 4th level spell slot (out of 1 total at 7th level).

No the decision is not so clear - 4th level slots are powerful and I'm giving up my only one but 2 2nd levels are more flexible. Hmmm. Now we're starting to look balanced. Particularly when you consider that as you go up in levels you get more 3rd level slots (2 at 8th and 3 at 9th+). Having the relative advantages change as you level up is also a good indicator of balance.