I do think wet sanding or even using a circular polisher are OTT for a car in good condition. I am no expert but am happy with the results I have on my red MINI.

If I were you, I would wash with Fairy Liquid to strip the old wax. Rinse and clay bar. Use a paint cleaner/sealant (e.g. Klasse AIO) or if you are able to wax often enough, just wax it.

I like P21S, but it does not lasy very long so now use Collinit 476S. Really easy to use, finish is great and durability seems very good.