I'm 42 years old---the answer to live, the universe and everything---and I've been visiting music stores since 1986. I've seen all the advances. With regards to the last 15 years, well, sampling has improved a lot; however, what's driven that is the use of modeling to incorporate string resonance and damper resonance effects. Yamaha have created a new sampling methodology called Binaural sampling. Now, whether that bears much relationship to binaural effect, I don't really know; however, the sound clarity has improved as a result on their pianos that use it.
Action wise, there has been a revolution in the last 15 years.
The introduction of real grand piano actions in to digital pianos: Avant Grands (N1X, N3X); Novus NV10 and NV5, and sort of the Casio GP510 and GP310 models.
If you've got more money than many, you can also play real acoustic pianos with digital piano at night (silent pianos) and even have pianos whose strings and sound-board are used to amplify the digital sounds (Yamaha Trans-acoustic). That's all new.
With regards to digital actions (non-hybrid), there are two sorts: folded and unfolded. Folded actions have undergone significant improvements since 2009: both Roland and Kawai have undergone incremental evolution in their folded actions in both beginner and intermediate models. Unfolded actions have also improved considerably: the Grand Feel 1 action by Kawai (which I don't think was around 15 years ago) was a big leap up. It's been superseeded twice, so the latest action (Grand Feel III) is pretty good (CA79 and CA99). Yamaha have also improved their actions a lot in the last 5 years, but are perhaps still behind Kawai and Roland in their digital action design (still too heavy down-weight wise), with the exception of their top-tier CLP lines.
Thanks, I think I will have to demo the Yamaha Avant + Kawai Novus and compare to the Yamaha CLP + Kawai CA-X9.
I've been tempted to buy one without playing but you're right, I need to get in-store to try these.
It just feels like it could be years before that is possible. Well I guess if I've waited this long, what's a couple more years?