I'll share with you a non boat related (but solder splice related) story. A guy brought his beautiful street rod into my shop. The problem was that the fuel pump would shut down intermittently. When I was finally able to duplicate the problem, I traced it back to a connection that he had very carefully made with a solder joint. The car hadn't been together very long and had very few miles, so vibration hadn't killed it. The solder joint looked very good, the wires were all tight and the solder was smooth and shiney. Every now and then, the current flow would just stop. I replaced the joint with a good crimp connector (I use the ones with glue filled heat shrink built on) and the problem has never been back.
So even if you do a REALLY good job soldering, it's still not as good as a proper crimp connection.