So there must be one master in your proposal? Some slaves are write-only (display) but most will have data to give to the master when requested?
How far apart are these devices? I2C works for short distances up to 1m or so. SPI can work pretty well up to a few meters. RS232 works up to 100m but only if within the same building. RS485 can go kilometers.
These days, wireless radios are cheaper than buying 10m of cable. Have you considered one of the mesh network radios such as the NRF24 or Xbee?