This thread confused me quite a bit because it never explained why Conjure Minor Elemental (CME) is a problem - it was assumed everyone understood the text and the issue. Without that explanation, it is hard to see what could help fix it.
For anyone else like me: CME (4th level, concentration, 10 mins) adds +2d8 per attack you (only you) make into a zone, and increases +2d8 per upcast level. It's automatic (no additional attack rolls or saves). So casting this as a 6th level spell, for example, adds +6d8 per attack. The problem shows up when you can do something that does a lot of attacks as part of your action - like, say, Magic Missile. A level 1 MM with a 6th level CME does +6d8 x 3, or +18d8. That's more than 1.5x a 6th-level fireball (11d6). Casting MM at level 6 gets you 8 attacks - which means you're doing +48d8. That's 2 6th level spells that can't miss doing 8d4+8+48d8, or 244 damage on average. And obviously it goes up from there.
The problem in my mind is the "per attack" - that's where it gets messed up because it can get multiplied so many times. The obvious solution is to change it to only apply to "one attack per turn." The downside is that this nerfs it hard. By 7th level, all melee-focused characters are getting 2 attacks (at least) and many casters can throw two spells with a bonus action, so it seems like this spell was intended to do more like +4d8-ish on average?
My suggestion would be to change the base damage to 4d8, leave the +2d8 per spell level, and change it to "only one attack per turn." A 6th level casting still adds +8d8 to each attack over 10 mins, but this removes the massive scaling.
Anything that lowers damage or lowers the scaling damage but doesn't address the "per attack" lessens the impact, but it doesn't fix the core problem. +24d8 vs. +48d8, in my mind, is still the same problem. Limiting it to melee only encourages weird rule-manipulation in order to get as many melee attacks as possible instead of using spells like scorching ray or eldrich blast, which leads you right back into the same problem... and I feel like it goes against the spirit of the spell (to boost other spells).
Update: I didn't realize the spell also only affected yourself! Adjusted my reply, above.