I gave up on the raspberry pi and switched to x86 thin clients and usb-to-gpio adapters. A single second-hand Atom thin client combined with four usb-to-gpio adapters is cheaper, has more computing power, uses less electricity than four pi's put together.
Back in the day I would have used a separate PI for each project due to the limited computing power, but now I'm running the the equivalent of 4 PIs with a lot of computing power to spare in one box using about the same space. I haven't had any issues with any of the existing PI hats I tried so far and I might even expand to using arduino shields or extensions from other manufacturers since I'm no longer limited by the PI.
I don't think I'll bother with PIs again, this setup is a lot more flexible.