If I had my way I would solder every electrical connection, but honestly crimp connections will be fine. Afterall the contacts in the connector housings are most likely crimped onto the wires. I have some soldering experience and I must say that soldering two wires end to end is not an easy task especially if you are working in tight quarters. The trick is getting everything to stay put until the solder cools. You are trying to hold two wires together, apply the soldering iron to them, and feed the solder into the connection.

I don't personally care for insulation displacement connectors, even though we use thousands of these connections every day where I work. This is the type of connection that does not require you to strip the wires. You push the wire into the contact and it slits the insulation and makes contact with the copper conductors. They can be OK for low power connections, but I have seen these fail in high current applications.

Dan