Those two are the only wars I can think of with warships firing on other warships after WW2, and I wondered if I was correct.
If so, how do naval commanders, arcitects, planners, etc account for the fact that they have no or very little experience with modern naval combat when making plans, design decisions, etc?
There are several fights you are missing. There was combat in both the '67 and '73 Arab-Isreali wars, the former had the sinking of the Eliat by syrian missile boats, the latter had a major battle between missile boats.
https://www.idfblog.com/blog/2012/10/21/today-in-history-the-sinking-of-ins-eilat/
http://www.zahal.org/groups/battle-of-latakia
In addition there were several major incidents in the persian gulf in the 1980s. Operation MORVARID was a fight between Iranian and Iraqi missile boats and Operation Praying Mantis a significant fight between the Iranian and US navies.
http://www.iinavy.org/morvarid.html
http://www.navybook.com/no-higher-honor/timeline/operation-praying-mantis/
North/South Korea have had the odd clash. Two fights at the Northern Limit Line around Yeongpeong around ten years ago, each sinking a patrol boat, and one submarine attack which sank a corvette.
Greece/Turkey have similarly had the odd altercation, with the destroyer Kocatepe being sunk by the Turkish Air Force in what was arguably a 'whoops'.
I believe there was some minor scrapping off the coast of Former Yugoslavia during the breakup, the Russians beat up on the Georgians in 2008 sinking one of their missile boats, Sri Lanka had some naval escapades against the LTTE, and South Vietnam got beaten up a bit by the PLAN of China in 1974.
With regards to how they get experience - this is why extensive naval exercises are still held annually by navies that take the possibility of conflict seriously. A lot can be simulated in these exercises particularly since naval warfare is much more machine-dependent.