any experiences/feedback on the use of acrylic paper for standard watercolour paints or acrylic inks (diluted as in watercolour)?
Watercolours are best suited for use on watercolour papers as they offer the right amount of absorption for the watercolour paint but not too much that the paint sinks in.
It will depend on the absorbency of the acrylic paper whether watercolour will be successful as they need the surface to have some absorbency and some acrylic paper can be primed making the surface non-porous.
Acrylic inks should be fine on both acrylic papers and watercolour papers.
As always it is try and test to see what works.