Yeah, obviously I'm talking about stranded wires only. The only problem could be in the "insulation crimp" zone, since the total diameter increases dramatically. But solder keeps firmly the wires and solve the problem, as I understand.1) Crimp connectors are used with stranded wire. Depending on the stranding, you have that many individual wires attached. So adding a few more doesn't hurt, given the constraint of total wire diameter.
Bingo. You're again right. The major part of people against "multi-crimping" was referring their experience in a military "environment".2) As for solder, there may be specifications that forbid that. In aircraft, for example, when a crimped connection is specified, a soldered and crimped connection may not be. In general and barring such regulations, soldering probably doesn't hurt, but it may not help either to a well-crimped connection.