To me, the drool angle was a very important component, not merely superfluous, because it was used to let the viewer feel the approximate same uncomfortable feelings both the main characters felt throughout the series as they stumble and learn how to build a relationship between each other.
There's something to it, no doubt. Note how the ick gets de-emphasized accordingly: first it's a big deal, shown unfolding in gross detail... But the sequence is gradually cut in length, extra messaging is removed, and we're only left with a qick sign suck on a finger. But it all comes back for Oka! Because she's new to the ritual obviously. Then she brings two bottles when Urabe trains for the relay.