[Porsche-O-Phile]

“Code” could have been a case of the permitting authority or F.D. simply saying “put one in” and nobody bothering to challenge it or ask for a code citation. Happens all the time. I agree it’s not a bad idea given how you describe it however it’s fairly uncommon to see sprinklers in residential construction. Conventional wet-pipe system I’ll assume? Is there any kind of central fire alarm system?

Two HVAC units is a bit odd but not terribly so (depends on type(s), overall size of building and areas / zones served, etc. Also could’ve been related to not wanting to install a unit over such-and-such size to avoid triggering some requirement (AHJs were starting to tinker with energy codes and establishing new requirements for energy use in the mid-2000s so weird things like that came up sometimes.)

Central vac. is a luxury item - nice when it works, pain in the butt when it doesn’t. Make sure someone changes the filter and empties out the collector occasionally.

Basement ceiling as gyp. is probably a good choice IMHO; lay-in looks pretty tacky / institutional and isn’t a good choice for an area that can see moisture unless you use tiles intended for that purpose - and a lot of contractors (particularly residential) either don’t know the difference and / or are too cheap to actually provide moisture-resistant ones). Could’ve been installed looking ahead to finish it as habitable space or installed later by a P.O... Hard to know for sure.

I wouldn’t say any of those features are necessarily bad. At some point a wet-pipe sprinkler system will need to be replaced (usually 40-or-so years) so you’re good for a while if it was built in 2005.