I do have a 5+' Kawai grand that's about 25 years old but very well maintained: tuned and serviced more than once a year (i.e., my partner who's a professional musician and teacher has one).
You are right that Pianoteq or any other software-based solution will never be as realistic as a good acoustic piano. Even a Yamaha U1 is in some ways more "alive" than either a sampled or physically-modelled piano and has its own unique pleasures to offer over digital instruments. Even if the modelling was perfect, the sound having to go through a speaker system will have its limitations.
You are also correct that digital instruments done right are in many other ways superior to acoustics. Modern high-end keyboards like the VPC1 or MP11 are a joy to play, offer amazing control and speed, and in combination with state-of-the-art digital sound generation, like Pianoteq offers, they open new doors. Physical modelling seems to be one of the most exciting ways forward for digital musical instruments. My partner playing Pianoteq on my 10-year-old Yamaha P-140 (a budget keyboard) said that "it feels like cheating" because in terms of expression it was so much easier to control the sound than on an acoustic instrument.
I tend to think of physically-modelled instruments as a new class of instruments, even though I often do use Pianoteq as a substitute for the acoustic piano.
When the tonewheel organ (Hammond) was invented, it was meant to be a less expensive substitute for pipe organs. It did appallingly badly at emulating a pipe organ. But over the years, it became a deserving unique instrument in its own right and I see the same thing happening again with virtual/modelled (non-sampled) instruments. Difference is though that modelling also offers very good substitution options for acoustic instruments.
3/2 = 5
