It's definitely limited; I don't think there's any "finish" mechanism, but the most efficient way to get everything out of it is to first get one Hell card and use it on the first door - this card makes the room regen encounters while you're standing in it. The first room will only regen one encounter, which makes it relatively controllable even if you're underpowered. Grind out a few kills and get 7 cards of Fate and 7 of any mix you choose of Armoury, Coves and Data - the latter three spawn chests. Armoury chests hold, appropriately enough, grade 4 weapons or armor; Coves chests hold recovery items (or pots, etc); and Data chests hold - stay with me here - data cores.

Once you've got these cards, run through the whole house and spawn the chests. Each room will only spawn one set of chests, so you need to choose which type of item you want to get and use the appropriate card. Then you can either walk back or warp to Leonhart and jump back in to get to the entrance; go back in, start using cards of Fate on every door. This spawns an encounter with a mini-boss, which has a chance of dropping a Growth Ribbon. If you save-scum every encounter with them (only one per room), you can get 7 extra Growth Ribbons, bringing the total per playthrough from 5 to 12.

After that, you're basically done here. You can use another card of Hell on a door to get respawning encounters if you want to grind some more. Oh, and the cards of Heaven make the room spawn a save spot, which is almost entirely useless.

edit: Not 100% sure how, or even if, the Data chests work. I've gotten one data core from one, and mostly just blank messages when I tried others. I didn't really care enough to experiment with it, since by the time I got here I was already almost done with the game, just wanted to get all the growth ribbons and get out.

Many thanks, that's helpful. I had figured a lot of it out on my own in the meantime and I think you can use cards of Fate repeatedly to get more and more growth ribbons, though I haven't tested as much.

Which brings me to the next question, since you seem to know your way around in the game:

How do you bring down the fire barriers in the Summit. I know there is levers and you can push them, though no idea on how you actually bring down the barriers. I suspect there are more levers but I don't know how to get there.

Or maybe you have to finish the Grindhouse as when you meed the Scarred SilicAI he tells you to go to the Grindhouse and even though I've unlocked rooms until there were no more doors he still tells me that. Any way to progress, or is that just permanent?

Do I have to defeat the scarred SilicAI to do it? I found a mysterious crystone that transports me to an encounter with him in my house from some guys who kinda got in there without permission...

I'm not sure there is any way to bring them down; I may seem more knowledgeable than I am, since I just managed to figure out how to actually get to the grindhouse yesterday. :P A prior thread mentions the same problem you're having, that the whole place just seems... unfinished. That might be the point, I guess. I haven't actually played through a NG+ to know the details yet, but from what I understand the whole place was built by that scarred SilicAI, who may or may not be Darkstrike. If anything would give you more details about it, I expect the encounter with him would be it.

One thing I am fairly sure about, though, is that you can't use cards of Fate repeatedly. If you can, it's a very low chance for the boss to respawn; I just went through it again a few times, using cards of Fate at every door, and didn't see a single boss repeated. One of my old saves from before I sold off the cards had 46 of them, so that's about a 2% or lower chance most likely? I don't think it's possible at all though. IIRC a prior thread mentions that they're limited as well.

Hmm, maybe I got confused about all cards of Fate since I might've used them on different rooms, though I think I had the same boss in the same room multiple times.

Anyway, it was like this: After playing on NG+ I entered the house I bought after I had rented it out and a player in there gave me a mysterious crystone with which I could enter an unknown zone that lead to a Bossfight (not sure how high-level, all I know is I got destroyed at ~mid-level) with the Scarred SilicAI. I think there might be a continuation though I've got to play more to find out.

Totally forgot the point of the latter part: The player that is in your house gives you the crystone with the specific note that this is how you get to Darkstrike (if I recall correctly)

Ah, ok... anyway, the dev says, "This player gives you a Mysterious Crystone, which takes you to confront a character that may or may not be Darkstrike," so I'm reserving judgment until I finish the series.

Meh. Definitely not helpful as far as further plot exposition. I just tried him at level 35, not too tough with a well-geared caster party... very nice exp, about 15k, and a decent title - but it doesn't seem to do anything to advance the plot or shed any more light on the Summit or the Grindhouse. Jay just comments "That was Darkstrike? Somehow I don't think so." and you're left with the Crystone and an empty room. Dunno if the fact that the Crystone isn't destroyed means something, for many of the sidequests they are... but if there's anything more to this one, I'm clueless.