Interesting, that is certainly a mix of low tech and high tech- solder blobs, who knew?
Good point on the last paragraph, seems the simplest is a 12VDC bus with suitcase connectors or similar.
Note that the receivers will need a source of DC - it looks like 12V DC for what you show. If wiring simplification is the issue, I suppose there is some consideration as to whether you have a single 12V DC bus running around the layout...or whether you locally regulate Accessory AC or whatever to 12V DC with an AC-to-DC converter module at each relay receiver module.
