Must of above post now edited, but, to clarify, ZP90 still has digital outputs.
http://www.sonos.com/whattobuy/ZP90/You mentioned that neither extra network coverage or smaller form factor is of no benefit to you, so I see no reason to change. It it ain't broke...
Also interested to hear why your dealers think ZP120 has lesser amplification. The ZP120 uses digital amps which helped shrink the case size. IIRC, when G95 got digital amps, there was much said on the subject and performance cannot be compared simply by looking at spec sheets. Unless, horror of horrors, they have done a blind A/B comparison of ZP100 vs ZP120.
[plug]However, if anyone is interested, whilst stocks last which are going fast, I can get a great price on the ZP100/ZP80 bundle as long as I order more than one bundle. The discount on new bundle and units is still very good.[/plug]