Stock exchange sucks because it basically reduces something which is so complex and interesting - allocation of capital, international finance, allocation of risks - and just turns it into flat gold. Boring.
All of the mono-yield districts have to fight against this issue. More nuanced districts like the harbour offer more interesting game play opportunities. For the mono-yield districts, you need to work harder to make them interesting.
Looking just at the Commercial Hub and it's districts, the positives are:
- generates Great Merchant points, who have varied abilities
- can lead to a trade route (if not taken by the harbour), which opens up lots of game play opportunities
- Markets and Banks can benefit from City States, which adds interest to the City State mechanism
- provides special adjacency bonuses in some circumstances (Harbour, Hansa)
With a bit of work, you could add other interesting effects that lessen the degree to which Commercial Hubs are focussed on making gold, and make them more gold+. Other districts getting the same treatment could add gold to their potential output, depending on you choose to play them.
One route to do this is through more optional buildings, so you choose between building A or B (or C) at each tier. Ideally the yields of those buildings would vary based on the map (adjacencies, resources in that city, etc.). The aerodrome would be really well suited for this, with the ability to boost military, gold, tourism, etc. depending on what you add to that district. Other districts could get this treatment, too.
For the Tier 3 buildings, I assume the dev team expects the power system to be a boost to them, both in usefulness and interest level. I don't think it goes far enough, but a step in the right direction is still a good step. I'd like to see "per pop" bonuses come back, and Tier 3 buildings would be ideal for this. As someone noted above, policy cards that benefit specific buildings could potentially work to both boost Tier 3 buildings and give them more interesting game play impact. Something like "Venture Capitalism" could provide Science output from your Stock Exchanges and Gold output from your Universities, for example.
