I would suggest making conventional industries construct-able and cost only wealth, though a large amount (say 500?)
Basically you have an option to spend wealth and time to reduce the cost of structures (via the upgrade route), or get some benefit out of a population without having to spend TN resources.
It would still be much better to build TN structures directly, mainly because a 500 wealth cost would translate to taking long to build (especially since you needs to build many CI to get a decent effect. )
Also TN structures are much better at being specialized anyway.
(Sidenote: I would also increase the cargo size of CI to be much larger, say 125000 or such, to keep TN structures a more appealing prospect, even for moving about. )
It should only entail a single SQL command / change, so little effort.