An ESR meter is the *only* worthwhile way to test electrolytic capacitors. The capacitance function on a multimeter is useful for identifying unmarked capacitors but it won't tell you if the part is any good. I bought one about 15 years ago and use it all the time, but I do a lot of repair work. If you just want to fix a few things here and there, you might be better off using the shotgun approach and just replace all the electrolytic caps.

In terms of vintage macs and peripherals, it should go without saying that *all* surface mount electrolytics need to be replaced, and they should be replaced with dry tantalum or multilayer ceramic types now available, these will never leak and corrode your PCB. Every 68k logic board and NuBus card I've seen recently that uses these has had them start to leak, they were only rated 1,000-2,000 hours to begin with and the specs are lousy even when new. Most of the through-hole parts seem to hold up well, the exception being those used as output filters in switchmode power supply circuits including the horizontal scan and high voltage area in CRT monitors. 90% of the dead power supplies I encounter have bad capacitors and spring back to life with those replaced.