I love the idea of gp=downtime/training=xp but in actual practice, a lot of the time it's expedient to level characters up in the dungeon. Sure, a lot of medium-large dungeons are designed to be approached in multiple delves reinforced by that neat old-school restock mechanic, but sometimes they're down too deep, they've murdered half the dungeon and looted thoroughly, but they're about to hit a mini-boss or boss fight designed for the 5 or 6 part of "A Dungeon Adventure designed for 4-8 characters levels 4-6". Or stuff like B5 'Horror on the Hill' designed for characters levels 1-3 but you're likely to get dumped down the trapdoor and trapped in the three level dungeon at 1st level. There's a frickin DRAGON blocking the exit! If the PC's have the XP to level up in that dungeon, you're going to do it.
I think in 1e that was part of the point, to keep the party from leveling out of the intended range for the module and/or to slow down progression in general. Remember there was also a rule that, not only couldn't you gain a level until you trained, but you stopped receiving experience.
You also end up with this tension between wanting to clear a dungeon to prevent restocking between sessions, and wanting to level. And then, because of the nature of training rules, the amount of time (and cash) you spent training increased based on the DMs (arbitrary) assessment of how well you roleplayed your character. So roleplaying well (by the DM's definition) is incentivized to save money and limit the amount of time for the dungeon to restock.
I practice I think this is part of the reason you see, in discussions of early Gygax games, a tendency to only partially complete a dungeon, then go do something else, then come back to the dungeon later. (The other factor being that it was easy to miss things, and sometimes you wanted to go back to find what you had missed.)
Re: B5, and getting stuck in dungeons in general, them's the risks you take and why you need to husband your resources. Also, patience helps; dragons sleep a lot, and aren't there the whole time. At least that was 1e dragons, I don't remember with B+.
Truthfully, I think modern games level too quickly. People want the fun of levelling and are poor at delayed gratification, but then I notice players and DMs getting bummed that they level out of certain areas/experiences, and there is a pretty short time limit on the whole campaign. When we played monster XP only (no GP=XP), we could keep those campaigns going for years, even though we were probably playing 12 hours per week.
, the dragon breath weapon change is an interesting departure.
