Vintage Synth Repair

Im defintely of the 'if it aint broke dont touch it' school with caps. 

Yes of course electrolytics break down with age, but temperature and on-time have a huge role in accelerating that too.
 
I repair vintage arcade machine monitors for people. I re-cap every monitor as a matter of course. Many caps are shot in this situation. Re-capping fixes maybe 25% of faults and usually makes the picture look a bit better too. The monitors are subject to high temperature, high voltage, and very long on-time so it's not suprising.

I have to say in Roland synths I would never do such a thing. The rewards for doing so really are negligableas far as i'm concerned. They are on the whole still perfecly servicable...much more common to find bad sliders, pots, buttons..transistors, etc in this situation.

I Just troubleshooted a VP-330...bad SAD1024, SAD512, 2SC1815, BA662,..30 years old and the caps are still working fine..

But then take the Arp Omni and it's another story....the tants are terrible in that machine..as are the cmos IC for dying in that beast...

I just take it case by case using my experience(and others) as a guide, but I would never automatically cap everything just based on it being over 25 years old.