"Elbow,
having compared both at the factory on my old 252 with the same Burndy and SNAIC5, I'd say that differences are only fairly marginally in favour of the Supercap2. Internal differences are pretty insignificant barring the new, and supposedly better sounding, switch. Of course, even when things remain pretty much the same, Naim never stands still in making detail improvements. I'm sure the better casework and improved feet make a difference too. However, bear in mind that at the time my NAC252 was fresh off the line and not run in, so my findings may not be definitive.
Worth remembering that Naim used to offer a cosmetic upgrade for the Olive Supercap with a new style fascia that also includes the new switch (but not the feet - they won't fit). It's was not exactly cheap though, so may not make financial sense against a similar second-hand Supercap2. Not sure whether this is still available but a quick enqury to Naim should confirm or not."