Response to this thread has all been very helpful for me, I appreciate everyone's input!
Now that i've looked it all over and thought about it, I think much of my completed work on this dungeon is useable with a little tweaking. I'll also be incorporating some suggestions here for creating new motivating hooks for he PCs.
The main cautions I'm reading are:
- Get player buy-in.
- Make clues blindingly obvious.
- Offer multiple reasons & modes for delving.
- Not let the adventure be pointless for the PCs!
Most of that, I think, is manageable by diversifying the reasons the PCs would be exploring; and by really highlighting clues.
I think my main goal as GM, in this case, is probably to just make a serious effort to avoid the whole "tricked by the Red Herring" problem, without unabashed player buy-in and a very good story reason. For the most part, if PCs encounter it, and if that deception would foil their purpose, then I'll "strongly hint" they're not done yet. OTOH, if their particular hook doesn't even concern the historical BBEG or MacGuffin, they don't know it's a red herring, and the issue goes away. And whatever hook they
are pusuing, I'll be especially attentive to reinforcing that hook's themes and marking relevant critical (eg, "bottleneck") clues with flashing neon signs.
(FWIW, this particular dungeon is intended more as a (transient) hex feature than a critical campaign plot point. It's around 8th level, so not particularly earth-shattering, but offers decent treasure, a little renown, and an opportunity or two to gain a patron or nemesis. The real BBEG is completely sequestered, incommunicado, unable to orchestrate much within the dungeon much less outside it; therefore, he's in a bargaining mood... which is always helpful for future campaign development.)
Anyway, I'll be coming up with a handful of extra hooks (some directly relevant to the tomb's lore, and others simply incidental) that should cover most of my reservations regarding player buy-in and pacing. A good mix might even suggest reasons for PCs to revisit the site without a hamfisted "gotcha!" Between that and marking/adding relevant clues, and maybe intertwining some hooks for added depth, I think this will be a decent dungeon to throw at players.
Again: Thank you, all!