The Cap's µf rating determines if it is a high frequency cap or not. You should stick with the SAME µf rating to make sure that the circuit's tuned to its desired frequency.
What you should change (and to a greater value) is the voltage the cap can handle. As an example, lets take those dreaded 47µf @ 16V can caps that leak all the time... when replacing them with a higher value cap, the 47µf stays the same, but using a 20V or 25V cap will make it better able to handle power surges and energy ripples in the circuit and keeps it in tune to its proper frequency better, and thus they last longer too.
Yes, using a solid state cap will make the Mac last about 20 or so years, but think of them as a bullet proof vest. Each time it gets hit, it weakens until it is unable to unprotect you anymore. Thus a higher voltage cap, like a thicker bullet proof vest, will be able to take more hits and last longer. 30 years or more. But do not let it fool you, shoving a 50V cap will not work because it cant physically fit and requires more voltage to work. A 20V cap replacing 16V cap is "good enough."
One of those analog bard caps is rated for 4000 Volts. You can put in a 4500 or 5000 volt cap in its place, as long as the µf rating is the same. Note: For these high voltage caps, there are no solid state replacements so you are stuck with "liquid in a can" cap.
You should also talk to TechKnight about EMR Rating of caps, which is another subject about caps too long to discuss here. He can explain all about it to you... just be prepared to grow abut 3 pounds of brain matter to store all that information!
