I was wondering if this houserule actually helps the Mass Cure spells in any way.

[Dunsparce]

It's one we've been using in our games for about a year now in 3.5, basically we lowered the effective spell level of all Mass Cure spells by 2

Which means:

-Clerics get Light/Moderate/Serious/Critical at spell levels 3/4/5/6
-Druids get them at levels 4/5/6/7
-Healers get them at levels 2/3/4/5
-Bards get Light/Moderate at levels 3/4 and now have access to Mass Serious as a level 5 spell and Mass Critical as a level 6 spell

I know they still scale like butt, but does that make them at least slightly more useful, especially in respect to Wands/Eternal Wands?

[Venger]

It's one we've been using in our games for about a year now in 3.5, basically we lowered the effective spell level of all Mass Cure spells by 2

Which means:

-Clerics get Light/Moderate/Serious/Critical at spell levels 3/4/5/6
-Druids get them at levels 4/5/6/7
-Healers get them at levels 2/3/4/5
-Bards get Light/Moderate at levels 3/4 and now have access to Mass Serious as a level 5 spell and Mass Critical as a level 6 spell

I know they still scale like butt, but does that make them at least slightly more useful, especially in respect to Wands/Eternal Wands?

Not really. They still offer no advantage over the vigor line. The issue isn't just the cost. It's that the effect just isn't something anyone wants or needs.

[Gruftzwerg]

Not really. They still offer no advantage over the vigor line. The issue isn't just the cost. It's that the effect just isn't something anyone wants or needs.

This. Healing actively while in combat is a trap.
You want to avoid healing in combat for either preventing damage (crowd control spells) or do damage by yourself (and end the fight sooner, so you don't need to heal that much).

Off combat healing is mostly done by clerics spontaneous casting cure spells at the end of the day with his spellslots left.

In-fight the only situation that demands a heal is to save a teammate from dying > big single target heals.

And if you want to use it to heal more efficient / with less resources it fails at that too. It's high spell lvl is a to high cost. If you wanna be more efficient and spent less spellslots for healing, use "Touch of Healing" Reserve-feat to heal your teammates up to half/maxHP all day. Than you need lesser single target heals to cast.

[Flickerdart]

Maybe if all cure spells were mass at their regular levels, I'd use them to top the party up against a fireball spewing enemy.

[Fizban]

Lowering them by two levels will indeed make them much more useful, but you're thinking about healing the wrong way. Nothing will ever compete with post-battle healing's "free"-ness, but if you want to heal in combat you need mass spells sooner. And healing in combat it a perfectly usable specialization no matter how much people tell you it's not, if you're actually specialized in it.

For comparison, check out the Insignia of Healing spell in Races of Destiny. It's already mass cure light at 3rd level except better in every way, so dropping the levels is easily justified.