New wonder for unurium seems interesting, but I'm still trying to compare it with the Temple of Spirits, as I have finished ch18 just 2 weeks ago and not really dived into building its wonders yet. With my current city layout on live, Vallorian Seal Tower would give me around 8000 unurium per 3 hours (+ decay reduction), which is around 448.000 unurium per week (and I have quite a lot residences, there is still a bunch of players who rely more on event cult+pop hybrids). The Temple of Spirits would bring me with the same city layout around 672.000 unurium per week (spire only). I think this really plays for the Temple of Spirits, also considering the fact that unurium is especially difficult to produce (as it replaces seeds then), and with the ToS' both effects actually giving unurium, that need of producing it in trader could go away more likely with ToS, than Vallorian Tower.
(Calculated with both wonders at level 35 - I already have enough KPs for that, as there were no interesting wonders for few last chapters (16,17)).