> I've read that electrolytics actually degrade faster when they are not
> used close to their voltage rating, ie, a 35v cap on a 5v line - though
> I can't remember where...

Aluminium electrolytics rely on aluminium oxide dielectric formed between
the aluminium electrode and the electrolyte. This oxide can disappear if
the caps are not used properly (or stored for too long), causing leakage
or a short. It can also break down at a lower than designed voltage.
Reversing the polarity will eat away the oxide ...

Older large caps (ca. before 1970 I think) used to require a 'forming'
time, where you'd connect them to a current limited PSU and have them at
1/3Vcc for a few hours, then 2/3Vcc for more hours, and the at full
voltage for some more time. This re-forms the oxide. The method is still
valid when restoring very old equipment. It can save you a big bang and
smoke.

New caps don't really need this, and they are not expected to last that
long in the first place (try to imagine some all-plastic contemporary
equipment in 10 years).

Most tantalums used in consumer equipment are (wisely) not employed as
supply filters, but as bias decoupling and as coupling caps or timing etc
caps, and are not subjected to voltage and heat abuse. They last forever
(>30years in correctly designed equipment in my experience). More recent
miniature equipment uses lots of tantalums (or other solid dielectric
types) in SMPSUs in addition to other roles but they are of special type
(ESR and voltage and current ratings etc). They do not cause problems
afaik.

Peter

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