I think it's also worth pointing out that on every single spell that has upcasting benefits, it says something like this:

Using a Higher-Level Spell Slot. The damage increases by 1d6 for each spell slot level above 1.

It says there very clearly that those benefits apply when using a higher-level spell slot. And if you're not using a spell slot at all, you're not using a higher-level spell slot, so this part of the spell description doesn't apply. This is, I think, specifically why they changed the wording of these things (which used to just say "at higher levels" instead of "using a higher-level spell slot").

Quote from wagnarokkr >>

I think it's also worth pointing out that on every single spell that has upcasting benefits, it says something like this:

Using a Higher-Level Spell Slot. The damage increases by 1d6 for each spell slot level above 1.

It says there very clearly that those benefits apply when using a higher-level spell slot. And if you're not using a spell slot at all, you're not using a higher-level spell slot, so this part of the spell description doesn't apply. This is, I think, specifically why they changed the wording of these things (which used to just say "at higher levels" instead of "using a higher-level spell slot").

It is also worth noting that for ongoing effects, there is always a benefit to using a (small) higher-level spell slot since the spell level sets the DC for Dispel Magic attempts. There may be other niche benefits as well.