Mod my Citation amps?

Okay, this is a thread about modding Citation 5.1 and 7.1 amps.  I have two of each amp and they are starting to get a little long in the tooth.  They were used and new B stock when I bought them 15+ years ago.  So the newest of the group in about 16 years old and the older ones are approaching 20 or so.  Given that their capacitors will need some servicing at some point anyway, and given that that point is rapidly approaching, is it worth it to mod these amps or merely replace the caps to lengthen their life.  Whatever I do, it needs to last another 20 years.  I have no intent on replacing these amps and the shipping will be the same (by that I mean quite a bit) no matter which choice I make.  So it is really down to what do I decide to do with these babies.  Also, if I mod them, how far do I go?  This isn’t something I can easily audition, so I need to get a sense from people who’ve modified their own amps what their improvements were like and so on.

thanks for any feedback!