Tom,
Not a direct answer but as no one else seems to be biting here's my 2p.
I replaced the SLEC (?) caps. in my NAP 250 this weekend with Kendeils courtesy of LesW. The amp is about 10 years old so was probably due for a recap.
First impressions: not a night and day difference, still sounds like a 250, but a marked and positive improvement. Main changes were more 'snap' - better timing - and more bass. The former was unequivocally positive, the latter took a few hours of getting used to. The change in solo piano, which I listen to a great deal, was particularly noticable: sounds more like a percussion instrument, as it should, and the left hand became more prominent. This alters the balance of familiar recordings and so takes some getting used to. I saw Mitsuko Uchida on Saturday and Arkadi Volodos last week and listened to recordings of them afterwards and I'm sure this is now more realistic.