Very nice production chains!
As for me, I have the same problem as you if I understand you right. I'm not a designer and I don't have any interest in creating buildings or graphics. So, I would love to have someone to create those, too.
I have thought about many ways to make the logistical part of TPF2 more interesting. One was the way to add much more various goods for towns to demand. But I don't like the approach of just carrying specific goods to a town, regardless of how many they are. With this approach, I would have to get every town every good as a demand and as we know, every good a town demands will result in +100% growth. To big towns will result in performance penalties. Balancing this out is possible, but will take time and makes game scripts more complex. And it makes failing more forgiven. If one line has a problem, mostly only one good will be missing for the town and so the town will still be very big.
Another way is a special good that consists of every good a town would demand. This way, town growth is the same as in vanilla, no game script is needed for balancing. And if you fail with one line, the final good will be always affected and so town growth will get a big penalty for every mistake. Another nice effect here is: industries that create this final special good will always need a big cargo hub. The only downside here is, that the start can be very overwhelming as you have to connect all industries to get the final good.
These are my thought. Good luck to you
MFG PMV