What products should I be using to clean and condition older dashes? The Skyline is some sort of vinyl / plastic and is very fragile. (Know to bubble and split).
There are a lot of products out there. What type of finish do you want? Do you want a one step or two step process?
What immediately would come to mind for me would be Gtechniq I2 triclean for cleaning and Gtechniq C6 matte dash for protection.
I2 is an all purpose cleaner that works on virtually an interior material (including upholstery finishes). It kills 99% of bacteria and is the best deodorizer I have used in an all purpose cleaner. This makes the surface clean for C6 which is your protectant. This product should be only used on plastics, rubberized pieces and vinyl trim. It will provide some UV protection, stain and abrasion resistance. To be clear interior protectants are a minor level of protection in the big scheme of things imo.
The above pairing will make your interior look matte/very clean looking. Both are easy to work with.