Before handling more esoteric suggestions, like what other critters to invent, how about we discuss some basic things (arguments hidden in spoiler tags):
1. "Pop an heir" is a useless action
It takes 60 turns. In the context of these games having a turn-over rate of about twice per week (for good weeks), this makes popping an heir take half a year in real time.
Meanwhile, it is possible to promote a unit to heir for a very low sum of money. Where "very low" means "less than what the city would produce in income during 60 turns". Since upgrading units is almost the only thing Schmuckers purchase, and popping heirs would block a city's production for 60 friggin' turns, I feel confident that NOBODY will pop an heir, EVER, and choose to promote a unit instead.
This makes this action useless.
2. Several Shockamancy spells are useless (to Shockamancers)
Several Shocka spells have descriptions like "treat as Variant of Hadouken, but with more cost". So let's see: same effects as a spell that ALL casters have anyway, at twice the cost? Bollocks.
This was probably put in so that Basic Shocka units (Knights, D-class) don't get too powerful. Fair enough, but one shouldn't nerf Shockas in the process.
3. Popping a Warlord is nigh-useless
The only reason to pop a Warlord is trying to get a caster. Otherwise, warlords take long to pop, are usually a worse kind of unit that what anyone can design as Knight class, and again promotion is better than halting production.
This hurts the game a lot for another reason: warlords are essential for almost anything that involves side development. Moving funds, exploring ruins, establishing cities and resource points ...
4. Resource points are nigh-useless
In the early game, particularly for a slow start (only the Chief and maybe one L1 city), they are indeed essential.
Otherwise though, once you get a few economic powerhouses, aka high-level cities, it really is waaaay too boring to have your chiefs spend months out in the field, just to establish mines that deliver a mere fraction of what the cities deliver.
5. The game is too damn slow!
And I won't spoiler hide this one. It takes 5 turns or whatever to pop a mine. It takes 8 turns or whatever to pop a warlord. Do you think anyone will still be playing in month 3, which is when, due to slow turn-over rate, we'll get to have a second warlord?! Second warlord, yay. Now I have two
people to send out for months at a time to build mines.
Be realistic. There's no way a human GM can manage a whole Erf sim in such a way to balance high turn-over rate, real-life commitments, and several players who have yet to post their orders. Think in these terms: two turns a week is the best you can hope for, so make it so that a lot can be done in two turns.
I've started playing two Erf-sims game, and watched a third. NONE survived to the point where players actually did something interesting like campaigns. I'm playing another Erf-sim, which I fear will go the same way. The speed issue must be fixed, pronto.
The whole point of this is lost if you keep it a secret.