My friend, I can personally guarantee you the 1Z only took 10 min longer to "Research & Develop" than the 1A did. And I'm also sure AK380 took no longer to R&D than the AK's before it, given each AK release happened within a 1 year window, yet each still got an unhealthy price hike...
As you already know, there is only 4 simple changes to the 1Z over 1A, I will now give you the play by play of what happened at Sony HQ between lead designer Hiroaki Sato and his helper disciple:
-R&D for Copper chassis: Disciple-" Oh noes Master, AK have an all copper dap". Hiroaki- "Oh yeah? We'll go all copper AND gold plate that ****". (But I'm sure they would have gone copper regardless of AK as it was the logical step from the ZX2 design ethos). 2 min "R&D" to switch out CNC bit for one to mill copper.
-R&D for Jack wiring: Disciple-"Um Master, what should we do with all this spare Kimber Kable we have lying around?". Hiroaki- *Thinks about strangling disciple with kimber kable, eventually says "We use it in the 1Z genius, while the 1A can use the same cable as ZX2." 2 min "R&D".
-R&D for Power supply capacitors: Disciple- "Master, we have these new FT caps from the lab". Hiroaki- "For 1A we partially use FT caps to help secure it's performance above ZX2, for 1A we'll use FT caps for the amps(4+4=8x FT caps), but for the power supply we use os-con caps from ZX2 . For 1Z we'll use FT caps for the amps and power supply both, which will give 1Z an edge over 1A. Disciple-"You are so wise Master, But which capacitors should we change?" Hiroaki- *Glares at disciple, "Idiot there are only 5 power supply capacitors, 5x FT caps for 1Z and 5x os-con caps for 1A. 2 min "R&D".
-R&D for Output resistors: Disciple-"Master you know how we use "fine sound" copper resistors in some of our AV receivers?(str-dn1070)" Hiroaki- *Slaps disciple, "Tell me that sooner you swine, we can use these on the 1Z amp's output." Disciple-*Cowers with hands above head "But which resistors do we change Master". Hiroaki-*Barely controlling the impulse to get out his Kendo stick and beat the crap out of disciple finally says "There are only 6 resistors total for single ended and balanced amp (2+4), so just change all 6 output resistors to "fine sound" resistors for the 1Z and have the 1A use 6 MELF resistors from the ZX2 instead. What I have to put up with ***..." 2 min "R&D"
The End
Based On a True Story (Probably)
Total R&D Time and Cost of 1Z over 1A: <10 min, $5.65.
Thus there is nothing in 1Z that would take any significant time to develop over the 1A as the changes are straight forward component swaps for higher performance parts that do the same thing, and these 4 changes alone must be responsible for any difference one hears between 1Z and 1A. These component swaps are indeed enough to obviously change the sound, but I'm not prepared to pay through the nose for them. I have nothing against those that are willing to, in fact I'm envious of you (in a way). But I'm awesome.
Now for actual R&D, engineering the circuit which both daps share, engineering the new FT caps and engineering the new S Master HX, would all need serious R&D time and cost, I see two scenarios:
1. R&D costs of this venture are all accounted for in the price of 1A seeing as it makes use of all said developed tech, meaning the 1Z is just a cash cow (AK style).
2. R&D costs of this venture are only accounted for between combined pricing of 1Z and 1A, making the 1A excellent value given it uses all said developed tech while being priced below singular profitability level, relying on 1Z to make up the profit margin. (Obviously this could be happening in various amounts, eg, half the profit on 1Z could be to comfortably cover margins in conjunction with all profit from 1A, while second half of 1Z profit is pure profit., etc. Either way it would make 1A good value comparatively.