(2) Electrolytic caps will eventually self-destruct. Just when that will happen is impossible to predict, but 20-30 years of service is pushing the envelope. Moreover, modern electrolytics are way better than those available back in the 70s, so swapping them in can have unexpected benefits in performance.
As I noted, since the caps are so cheap and so easily obtained compared to an IC that just plain does not exist any more, and since the service can be performed by a professional for little more than a couple of hundred dollars or by DIY for much much less, it seems foolish not to take this preventive measure.
I agree emphatically with Lewm and would add that if certain caps fail on Technics MK2 or MK3 during music play, the result can be catastrophic.
My MK2 had a cap failure just as I was about to I drop the needle and play some music. The platter was turning fine, but at high speed and in REVERSE.
I know this is cool for those that like to "scratch" but a bit risky for me.
One of my two Technics SP10 MK3s made perfect music for months and months, when a sudden failure caused the platter to suddenly accelerate to 250 or 300 RPM, I was blessed my Koetsu Coralstone was not in the groove when this happened.
My experience is based on four Technics total, two of which had failures that are potentially hundreds of times what new caps cost. As Lew says, it's just advice but I think my experience shows this kind of failure is not out of the question for products this old.
The upside is professional upgrades makes these super tables sound better than when they were new and pretty much protect you from these kind of problems.