You are not going to be replacing solenoids all that often, so I would question if there is anything to be gained by adding a connector.

If you mean all of the solenoids and switches, then you would save a lot of desoldering and re-soldering effort. But you would also be adding another point for potential failure in the circuit.

If you are going to do this, use connectors sized specifically to the wire size. You can purchase these at Home Depot or any hardware store.

I wouldn't do it myself.

Maybe Levi's not all that crazy.