The value of a boring NPC is that they don't eat up a lot of attention whenever they're in a scene, nor do they provoke the players to deal with them definitively, by for example killing them or enchanting them or whatever. This allows them to recur, and to become familiar persons to the party whose existence, however pedestrian, fleshes out the world and gives a concrete shape to incidental scenes that would otherwise be dull. It also pushes PCs to interact with people other than by threatening them, killing them, enchanting them, etc. Their very normality helps contrast with the more exciting components of the game and creates a change of pace and a sense of novelty with very little investment required on the part of the DM. Boring NPCs may be slightly antagonistic, but it should be the antagonism of a store clerk in a sour mood, not even the antagonism of a spurned lover or embittered rival, let alone a nemesis or dark lord.
Boring NPCs are particularly useful in locations that recur in a game. This is because they probably won't provoke the NPCs to do something illegal or drastic that then disincentivises them from returning to that location, or forces drastic changes to the location. They can also be extremely useful in dampening conflict from getting out of hand, or forcing nonviolent resolutions, which encourages roleplaying, and allows character conflict to avoid being resolved immediately by violence.
Boring NPCs also allow communication and information to flow. One of the more useful boring NPCs I have in my Emern game is a guy named "Pauly". Pauly is an innkeeper who knows everyone in Heshtown, and who gossips with everyone. Pauly's job in the campaign is just to be the CNN of Heshtown. He doesn't have a dark secret, he isn't secretly working against the PCs, or entangled in a rivalry with local gangs that will come up at a later point, Pauly is just there to be a familiar face the PCs can come back to when they return to Heshtown from an adventure. He's somewhat wise to their schemes, but he isn't invested in them, or in anyone else's, and he serves as a friendly but ultimately neutral point of information exchange.
Despite that description, Pauly is one of the most popular NPCs in the game, so much so that when the PCs returned from being knighted and give ownership of Jamaica, they invited him to a feast they threw in the front yard of their house. One of the reasons I think Pauly is popular is simply that the PCs confront horrific individuals trying to kill them and duplicitious bastards trying to chisel them frequently on their adventures, and Pauly is never one of them. Pauly is just an ordinary likable guy, the sort of person you could see yourself getting along with in real life, and this makes it easier for the PCs to get along with him, and because they get along with him, he draws out and enriches what could otherwise be dull scenes (like a celebratory feast).
Anyhow, give it a try. Insert at least one perfectly ordinary, non-adventuring person who interacts with the PCs on a regular basis (between adventures, or maybe at the start or end of adventures) but who isn't connected to the main plot and see how the party deals with them. You might want to make them a little useful (as Pauly's gossip is), to provide an initial incentive.