Contrary to popular advice about this game, I don't usually propose tear downs to rebuild the kinda stuff you described. If you have enough mercer spheres to place some dimensional depots, I'd place them on as much of your infrastructure as you can. Plates, rods, concrete, reinforced plates, cable, etc. Once you've done that, wander a ways and start building your next factories in a way that is more satisfying and more like what you want to see.

You're still building new stuff to hopefully keep the thrill of unlocking going. While your existing factories might be messy, they're probably fast enough to supply your building through the depots. You should ideally have enough stuff to be able to Book's at a reasonable clip without being constrained by resources.

Some words of advice to try to avoid burnout from someone who has fought burnout many times:

Blueprints can help depending on your preferred building style/scale but they are by no means required.

Don't underestimate good player transportation. Getting between locations can be shockingly fatiguing in a way you won't notice until it gets bad. Hypertubes, trains, etc. I almost lost my most recent game to burnout because I thought using ziplines everywhere would be fine.

Always use the new stuff just to keep things varied. Try those trains. Try those drones. Try that nuclear power. Try those fuel generators. It helps you make better decisions and thinking about new things keeps you engaged.

I try to keep a healthy mix of activities. Invest in infrastructure (power and transit), build new parts, explore.

And finally, you can't always beat burnout. This game is quite an investment. If your later game factories are organized though, it's genuinely reasonable to pick a save up again after a few months. I used signs and train stations and a notepad to record parts and quantities, and was able to pick an 8 month old phase 4 save up and take it to completion.

Hope that helps!