Burning Wheel tends to work on an assumption that the players will themselves introduce many of the significant NPCs.The PCs have to get to know the NPCs, or the rest of the story falls flat.
Not all of them, so I'm not meaning to contradict you - just to point out that different games and styles can approach this in different ways.
In my own case, even for NPCs that aren't introduced by the players, I generally prefer the introduction to take place in the context of some sort of conflict, then via exploration-oriented play - so if I was going to use an external threat to push an NPC into the spotlight, I wouldn't use a filler encounter to do it.
I don't mind this, but rather than "filler" would use a deliberately targeted encounter to do it.At the same time, I don't agree with a "drop all filler" policy - sometimes it's good to remind the players that there are other things going on in the world than their current struggles against the BBEG.
I agree that the players have to project their own meaning onto the encounters that make up the game, but I don't subscribe to the "My Precious Encounter" analysis of GM-driven situation, and - as a GM - I do my best to design encounters and scenarios which are ripe for the players to engage with, given their PCs and their prior disclosed interests.I think this line of reasoning also leads to the "My Precious Encounters" school of design. I don't believe every encounter needs to be particularly meaningful, certainly not from the point of view of the DM. The PCs may come away with an entirely different understanding of the significance of the encounter than what the DM thinks he's projecting.
I can't speak for others, but I find the adjustment you describe OK. I also don't mind the guards separately - at that point they're not just filler, they're a part of a scenario with which the players are engaging.What if instead of running into some low level opponents then later running into a higher level boss-type, you run into them all at once (a boss plus low-level minions). Does that logisitical adjustment make it more satisfying inherently? More satisfying for low-level character play? More satisfying for you? More satisfying for everyone?