Species houses need a buff because they have minimal impact and are too expensive for everyone to live in.
Now the Species houses give +3 resolve to whenever that Species has its own houses if everyone is in.
Which typically need 6-7 houses when you have the resources to build them(4-5 years in-game time).
When the game starts and in the mid-game, you are never going to gather enough material for those houses without thinking wasteful, it is not worth 4(6) Brick/Fabric/Plank for one house and 2 people. If one costs 6 materials, 6*7=42 Building materials, almost a service building with global benefits.
When you compare it with the Hearth upgrade, 8 Wood for +2 resolves for everyone, it just feels not effective.
When the game almost ends and you are gathering prestige you almost never need those +3 resolves and therefore never build them. Complex Food on the other end is easy to get and usable in the midgame for resolves.
1. Species houses make the favoring system CD quicker/more useful(+8 resolve) on those Species if everyone has their house. So you could get prestige from favoring more easily.
2. Numerical buff, Reduce the cost of building and/or get more resolve so we would build them mid-game. Value need to be considered carefully.
3. Production Buff if you are in those houses. +5% Production Speed or something minor.
4. Some Glade Events: The god of "Human"/"Lizard"
Must have X amount of Resolve for Species. Otherwise, The god will kill them. It forces players to increase their resolve for the Species.
I think you'll be glad to hear that in one of our previous updates, we added the option to upgrade species houses. Thank to the upgrades, you can choose if you want a numerical buff (like more housing space) or a species-specific production buff (like farming speed for Humans for example).
If you have not yet gained them as "essential buildings", the effect is indeed an little weak. But if you do have them as essential buildings (aka, whenever you start the them with that blueprint), then they are perfectly balanced.
I wouldn't like that glade event imo, it doesn't really solve the issue you're presenting.
I think #3 is the best / most interesting solution. I don't have a strong opinion on whether a buff is needed or not though.