The lizardmen economy is a bit weak compared to the other factions. Although the Silent Sanctum
buildings give some nice bonuses, they don't seem worth the cost considering the building cost and that you'll only benefit from many of them while you're fighting in the region.Could some of the silent sanctum buildings be upgrading to provide some income?
The Vampire Coast and Skaven both get additional income from their secret building mechanics and they provide some meaningful choices (with a rewarding payoff) for building these at the right location.
One way of balancing the cost would be to strengthen the geomantic web. This could activate whether you own the region or not, and the bonus would be beneficial even if you own the settlement.
Overall it seems like Oxyotl's campaign mechanics are weaker than (and has much less hype than) the Beastmen's, so giving the buildings more impactful, lasting buffs would make his campaign more fun.