Tomtv is right on here. Any exposed repair (the crimp connections and soldered connections included) should be enviromentally sealed to protect from corrosion which is going to increase resistance at the connection. Amp makes the heat shrink tubing and they also make it with a glue inside which melts during the heating and seals the connection from the enviroment.
For MSD use the crimp connections properly sealed will not be a problem. Stay away from soldered connections if they will be exposed to heat in their application. Other than digital buses and antenna leads for flight critcal systems the crimp connectors are used all over the various systems in the jet aircraft I maintain. Keep the number to a minimum and stagger them so when the harnesses are bundled you do not have any connectors drawn up against each other in the bundle. You can use gold plated connections if you are concerned about resistance, but you standard automotive wire quality (lower quality conductor) doesn't justify that.
Use the crimp conectors, seal the ends and use proper maintenance practices and you'll be fine.