I have plenty ugly to say about the 1974-76 models, but don’t have enough experience to comment on your ’79. But as for your powerpack, the simplest test is to see if it has spark (on both cylinders). If it does, the powerpack is working. They either work or they don’t work. Don’t fix it if it isn’t broken. And I’d say that overall, they are more reliable than the points system. Don’t fear science.

A tough call for sure. This engine is surely one of the ones with the funky grommet. If I had just inherited this engine I would surely pull it down and do the grommet, pull the head and do the thermostat. This vintage of the 9.9/15s is truly one of the best, and I wouldn’t want to take the chance of overheating it badly. Plus, I would be using it in salt water, so I would want to do what I could to service it extensively to stand up to salt water use and corrosion. If you decide to pull the powerhead to do the grommet, be sure to check the upper mounts, they are a weak link as well.
That being said, I can understand not wanting to "dig into stuff that aint broke", these things are a pain to work on, a lot of stuff jammed into that lower pan, and you run the risk of snapping off corroded screws. So, I would at least do a water pump job, be sure to replace that driveshaft oring and lube the splines with moly lube. Run the engine, there should be a strong telltale spray and any speed above idle. Keep in mind that these telltales create a lot of "false positive" overheat indications only because the line gets plugged up usually in the plastic nipple in the engine pan. If the engine cools OK, just make a point of checking the telltale spray at the start of every trip.
Like everyone says, the CD2 system is pretty much maintenance free. Bad grounds, and funky amphenol rubber plug connections can cause premature failure though. If you pull the flywheel, be sure to replace the plastic mag plate bushing (322435), and lube it along with the mag plate pilot bushing properly. A funky stop switch can cause ignition problems, but there isn’t much you can do to check/service the switch. Be sure never to cut the ignition wiring, or use butt connectors to repair wiring or connections.
These are great engines, the powerheads and gearcases are very rugged and reliable. The cheap plastic crap is expensive, so be careful with it. Be sure the tiller handle is properly lubed, and tightened, to avoid damaging those throttle gears.
Let me know if you decide to do the grommet job, I will help guide you through the process.
Don