Well well well....I think I have solved this issue.
So, let me give you a bit of context first. I have a 2009. 16k miles fully loaded Z. It's been garaged its whole life so you can imagine the dash had seen just a tiny bit of sun.
It was always good, but it was slowly fading as it's just old. I was wiping it with some wet wipes and then drying with a microfibre towel and sure enough, the dash was becoming stickier and stickier. I was going through forums, reading options, no solution.
Fast forward few months, we bought another daily for which I wanted to refresh outer black plastic trim and I got a product from some brand "Shiny Garage". It did the job phenomenally, which somehow stuck with me.
As I was preparing the Z for the new season, I went to get a new leather conditioner and I also looked for any dashboard products which would refresh it. I found one from the same brand, the product name is: Shiny Garage Plastic Protectant Matt
I've got no idea if it's available in the USA, probably you can get it.
So, I applied a total of 4 or 5 layers. Each time I did, I wiped the dashboard, then wiped it dry with a microfiber towel and it darkened the dashboard just a TINY bit. It did leave it non-sticky and non-shiny though. So I proceeded to do this several times during several days and the result is excellent. I'll post pics in a few weeks when the car gets out, so I can photo it in the daylight, but yeah. The sticky dash issue can apparently be fixed!