So true.
The first amp I built I used some cheap PVC solid core.
Like any first prototype it had a lot of component changes and soldering.
I thought I had it sounding pretty good then after some tweak I powered it up and it sounded like arse.
Long story short, the wire from the phase inverter to the power tubes had developed a break just inside the insulation where the wire bent down and under the board.
It was making intermittent contact and caused a lot of noise.
I actually found it by chopsticking around but it still took me most of a day looking at it and walking away to gather my wits.
I had simply fractured from too many bends and moving around.
So on an amp that you could build in your sleep, solid core is fine.
But on a new amp or one that is going to have a lot of changes, stranded wire may be better since it can handle more flexing before breaking.
But I suppose as long as you are aware of the possibility and try not to abuse it too much you should be OK.
Just be careful of the Red wire, it can sound bad.
