Though I typically don't run keys, I found a Marked Key and decided to see it's lucrative potential, for science. The following results include an approximate Flea Market value at the time of this writing. Beyond what's listed, the room typically contains garbage roubles and ammo. (Edit: Apologies for mobile formatting, I'm new to this.)
Weapon Case (1.2m)
DVL-10 (70k)
Money Case (270k) {contained Bitcoin (128k)}
Kedr-B (25k)
Ammo Case (120k)
AS VAL (70k)
1GPhone (37k)
Weapon Case (1.2m)
MPX (32k)
TT (8k)
SV-98 (22k)
SKS (14k)
RSASS (120k)
M700 (30k)
Gas Analyzer (18k)
AK-103 (35k)
MP-153 (18k)
Electric Drill (20k)
Weapon Case (1.2m)
TX-15 (80k)
Kedr (12k)
Weapon Case (1.2m)
Kedr (12k)
MDR (50k)
M870 (22k)
M9A3 (11k)
GPhone (12k)
PM (5k)
Nothing
SA-58 (50k)
AKS-74 (34k)
Glock 17 (16k)
MDR (50k)
MP5 (26k)
PM (5k)
M61 {x9} (8k)
Weapon Case (1.2m)
RSASS (120k)
M1A (50k)
MPX (32k)
Vepr-209 (15k)
AKMN (44k)
PM (5k)
7.62 BP {x13} (6k)
Magnet (10k)
Nothing
Documents Case (220k) {contained West 323 Key (80k)}
FiveseveN FDE (35k)
Ammo Case (120k)
DVL-10 (70k)
Vepr-209 (15k)
Vepr-Hunter (30k)
Magnet (10k)
M1A (50k)
MP5K (16k)
Total = ₽ 8,358,000
The key currently floats between 50k-70k, making my estimated profit 119-167 times it's value.
If you're unsure if you made it to Dorms first, you didn't. The fact that the doors are closed doesn't mean shit. Don't be this guy.
Building off the last point, Dorms is dark and lacks ambient sounds, so assume that every angle is being held by someone wearing ComTacs. Peeking hallways from the interior stairs is the most dangerous, because you have to cover multiple directions. I run plenty of flashbangs and prefire randomly, forcing people to stop looking at me or give themselves away in a panic.
Bring a kit, including a backpack that's at least 4×5. Being defenseless here is a terrible idea. Scavs spawn in the building now, and even if you successfully arrive before other players, you may have to fight your way out. And while it's possible that your raid is devoid of people, you will curse yourself forever if you go in naked and find a case that you can't pick up.
The two most advantageous spawns for running the Marked Room are at the concrete Main Bridge and at the train tracks near New Gas Station. I would say the latter is more ideal, because you don't have to navigate the Gas Station choke point with a Weapon Case on your back.
Both times that the room was empty, the Scav Boss was in the building. I've no facts to form a correlation here.
Lastly: Do not leave Dorms through the wooded areas if you value your life. It's the only location on the north end of the map that makes indoor sound effects, so if shit went down there, everybody heard it. Leaving the area is a nightmare when it's been a warzone for the last twenty minutes. For some, waiting in a bush outside is far easier than contributing to the fight; never underestimate their patience. Your safest bet is to take the street and head south to Construction, because you can more readily contest the angles presented to you instead of searching foliage. Bonus points if you grenade the building on your way out for confusion purposes.
Conclusion
In terms of my personal results, running the Marked Room was worth it. However, it's literally gambling. There's a possibility that you'll repeatedly find nothing, not to mention you can be involved in compounding circumstances resulting in a 40-minute bloodbath. So go in expecting a fight, because there's treasure and everyone wants it.
Right now there really is no point besides sandboxing after endgame, so how do you keep players that want to do things besides building? The team is ...