Danger Room Reward
I just recently did a Tier 2 Danger Room by myself, and it was actually very fun. I managed to keep myself alive by using an Antigua the whole time, barely pulling out my sword (because close combat = death) - it was pretty intense. However, I was somewhat disappointed by the reward at the end. I got less than half a quarter of the heat that I got from actually killing the monsters, and maybe 50 Crowns.
My suggestion is to make the reward much better than this, to motivate players into trying out these danger rooms more often, since most people seem to just complain about them being too hard. Perhaps double the amount of red boxes? Maybe make a new type of box that drops twice more heat/crowns than red boxes? Maybe give a nice good preset chunk of heat/crowns? Also, it would be nice to have a couple of heart spawners in the reward room, to heal up afterwards.
(It also seemed that the further I progressed through the danger room, the laggier I got. After I finished the danger room, I was at the point where I could barely finish the rest of the level.)
All in all, it just seems like the reward is anything but worth the trouble. At least, this is my experience so far; maybe I just need to go in groups more often. Anyone else?
Yes, groups would technically boost Crowns and Heat, that's true. At least, as a group, and even individually if you got to revive someone. I was only disappointed at the fact that the reward was a considerably lower amount of heat and Crowns than that which I got from actually defeating the monsters to get there.
Also, for the record, I believe I was on the floor just after Moorcroft (~Depth 8?). I also had all Lv1 3* Equipment, and apparently Antigua's are pretty miserable right now, so it may have taken me a lot more work than it would with the right gear...
All in all, my only concern here is that many Knights will just walk past danger rooms because they don't believe the reward to be worth the work (and the risk). Boosting the reward would definitely help with that, especially if you always stick a set amount in there. As I said before, for example, a preset amount of heat globs and- now that I think about it, heart spawners may not be such a good idea, considering Knights could walk back to the abandoned danger room for hearts whenever they wanted. Perhaps just set half-a-dozen big hearts or so? At least then there is a finite amount.

There should be numbered spawners.
Like, something will spawn on there, but the spawner has a count display instead of a circular arrow.
When the count hits zero, stuff stops spawning.
That way people wouldn't be able to camp at a respawning heart all day just to beat one level.
It could create some interesting puzzles as well.
I like that idea. It allows multiple items to be stored in one single space, rather than spread out and taking up more room. Two numbered spawners (for the visual symmetry) of 5 hearts each after a danger room would be nice.
what depth were you at? because it's essentially rule of thumb that the farther depth you are down, the more rewarding it will be. I'd say this is true for specifically arenas & danger rooms.
When I think of danger room rewards, I think of all the rewards from the multitude of monsters in such a short amount of time. I'll go ahead and assume that you did get a fair amount of heat from all the monsters. Not saying that you shouldn't solo, i'm completely for it. Groups definitely make it easier though (in most cases)