Isn't there another possibility, namely, changing the XP-to-combat ratio so that filler encounters aren't necessary?
Probably. But if you're doing that, I would suggest just dropping XP-for-combat entirely. There's not really any need for it, and it just gives the DM much more freedom in his pacing.
The first module I ran ... had the players join up with a caravan in a town and described days of journey before it got to the point that something happened (other than random encounters, natch). We're talking potentially hours of play before something significant happens...
See, it's difficult to comment on that without knowing what "something significant" means. If the key conflict in the encounter comes about due to interactions with the various NPCs in the caravan, than those "days of journey"
aren't filler - they're needed so that the rest of the module makes sense. (The PCs have to get to know the NPCs, or the rest of the story falls flat.)
On the other hand, if the adventure is really about some external threat to the caravan, then those "days of journey" are indeed filler. In which case, the thing to do is probably just drop them. But that's just bad adventure design. (Which, of course, I'm not going to defend!)
A lot of obstacles and opposition in modules is filler. It's there to take up time, to provide a reason for the niche skills of one type of character, or to make the experience seem "real." It's ok to leave a few of these in for old time's sake, but mostly, unless it's something your players will really get a kick out of, just go ahead and invoke the Say Yes or Roll Dice rule.
Sure.
This was writen about AD&D modules, but I think has remained true in more recent adventures too.
Yep. I recall running the first adventure in the "Savage Tide" adventure path, and being struck with the fact that there's a huge thieves camp (or were they bandtis/pirates?) that, frankly, just isn't very interesting - just room after room of filler encounters.
It was okay with that group, since we were playing weekly for six hours at a time. However, with my current group we play mostly fortnightly, for three hours a session. In that environment, my tolerance for filler is minimal. Indeed, I don't use pregen adventures with this group at all, as the assumed pacing just doesn't work for us.
(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.)