Semaphores will be easier to life extend than more modern panels with knackered wiring.
The most annoying thing is that the problems with insulation degradation of internal rubber wiring have been known for decades. BR knew of problems with some batch’s of wire in the late 1980s. Plus some electrical wiring for semaphore/mechanical areas was not in a great state.
But despite this, in a lot of places, until the insulation got to the ‘brown trousers’ state, no one wanted to do much about replacing the affected wiring.
In places where good quality PVC insulation was used, that’s still intact despite being over fifty years old. Similarly, a lot of the rubber insulated wires that came from good batches, is also still serviceable, again despite being very old.
And if the railways got their existing staff to renew the affected internal wiring before it got into such a sorry state (when special control measures have to be introduced), it could be replaced at a fraction of the cost of resignalling.
The bigger problem was the external lineside and tail cables. The rubber types in wet conditions typically only last twenty to thirty years.
Anyway, sorry for going off topic.