Realistically, in order to have Tall worlds, several things have to change to keep stuff in balance:
1. Raw production CANNOT be linear with population. It's just way too gamebreaking to do so. We've discussed several ways to fix this current 1:1 ratio, and while I don't have a total solution, I've tested one on my own that seems to balance considerably better.
Raw Production = .5 * (pop)^1.1
2. Improvements (wealth/production/research) have to have low, fixed values (i.e. +.5, +.75, +1, etc.) for the basic bonus, and modest % per level (e.g. +5% per level).
3. Approval has to be changed to a penalty system. You get 100% production at 100% approval. Any approval level below that reduces production. For example, use a linear step function, so for every full 5% below 100%, you lose 5% of full production. So a 43% approval rate gives a -55% penalty. To go with this, approval sources have to be more plentiful - e.g. bring back the starbase approval modules, but don't let them stack as high as planetary ones, and remove the resource requirements for "ordinary" (i.e. more than 1-per-planet) planetary approval improvements. It really has to be possible to have a 40+ population planet with 75%+ approval, and, with a bit of work, a 100% happy 30 pop planet.
What the above does is this: to get a Tall planet, you build mostly cities and approval buildings. This gives you very balanced values (i.e. similar adjusted wealth/research/production), but still sticking below a pure 1:1 pop:production ceiling, so a Tall planet isn't some incredible powerhouse, but rather a general "everything" planet. So, for a planet with 30 pop, you're looking at about 21 raw population, which means 21 production, 21 research, and 21 wealth.
For Wide empires, individual raw production for <10 pop planets is severely sub 1:1, and more like 1:2. There, you need to fill the planet with specialized buildings to get decent values, and you'll only ever get those for one category. So, presume a class-10 planet with 8 factories and 5 population, that would be 3 raw production, with maybe +4 and +100% in production bonuses, yielding a production of 14, but a research of 3 and wealth of 3.
In short, to support the difference between Wide and Tall, you need a population:raw ratio that yields more benefits per 1 of pop at high population levels than at low levels, AND you need individual improvements to provide substantial, but not overwhelming, bonuses. The goal is for Tall empires to consist of generalized worlds, and Wide ones of specialized worlds, with you needing somewhere around 3 Wide planets to equal one Tall planet in the sum total of output across each category.