In hand wired amps (which do indeed last longer, especially in tropical environments) the wiring is not soldered to the tubes. Just thought I ought to clear that up.
In a hand wired amp, the tube socket pins can move more freely, allowing the tube to adjust to dimensional changes due to heat. PCB sockets do not allow this. Hand-wiring also allows one to control inter-wiring capacitances, often resulting in greater bandwidth, plus the quality of the wiring can be controlled.
Heat is the enemy of tubes, wiring and components. If a circuit board is properly laid out though, heat should not be an issue.