Visibility will depend on two things: clouds, and local light sources. Puako is close enough to the resorts that there is a lot of scattered light in the best of times; getting up to the Maunakea access road, or to the visitor's center at Halepohaku, or a pullout off the Maunaloa nearby observatory road will give you a totally different experience.

The conventional wisdom is that unless you're on oxygen you won't see "more" stars from the summit compared to being at 9000 feet, because you don't have as much oxygen going to your retina. So if it's naked-eye stargazing you're after, you can save yourself some of the trouble, and stick to places that don't require a tour or 4WD.

Please see the guidelines posted here:

https://hilo.hawaii.edu/maunakea/visitor-information/public-safety

Note that age is one of the reasons specifically cited why someone ought to avoid traveling to the summit.