Haha, good one, I obviously don’t know out of my head which GApps version contains what exactly.
AFAIK the Play Store can update itself. I mean, do you think someone who has say a SGS8 only gets Play Store upgrade… well when? With their new firmware? Nope, don’t think so. Just a few months ago I have seen a SGS3 with Android 4.3 getting a Play Store upgrade. Via Play Store. AFAIK the same is true for all the other GApps, and I don’t see why some Android versions would be exempt. If Play Store supports that Android API version, it ought to work.
If you’re using LOS without GApps you cannot flash it afterwards. That’s always warned upon: install it now or never.
If you’re using microG, then you can use that to keep your applications updated.
So I still don’t see the point, hence why I asked
I do see the point of installing latest modem.zip, even if you already installed that version (ie. no changes). That way, you don’t have to verify whether baseband got updated or not. You just install it because, theoretically, figuring out if its updated takes you more time.