It seems some additional items are added to the Cistern when you complete certain numbers of additional jobs for the Thieves Guild, the highest reward being given after 125 jobs. I found them monotonous after some time and only did what was absolutely necessary. How many of these jobs have you done?

After i got the nightingale armor and completed the main quest, i left the thieves guild to the RATS

I did a grand total of 24 jobs extra as I didn't see the point in doing wasteful jobs... Maxed it at stage 4 and gained the guild master title... It's not a matter of one total number you have to do, it's a matter of doing 5 in each of the major hold capital cities (Solidude, Windhelm, Whiterun, Markarth) to unlock the special job for that city that gives the influence in it...

I also quit a large number of jobs that just kept growing to get the last couple of cities since I didn't feel like doing jobs in places I had already finished... As a result my thieves guild list of number of jobs completed is at like -17...

This

I only ever did what was required to become the guild master. Beyond that I just can't be bothered.

The additional jobs get repetitive fast imho. Also, it feels like they were added more or less as an after thought. To add some thievery to advancement in the thieves guild, because the thieves guild quest-line itself isn't much thievery oriented at all imho.

I did them till I became guild master then stop got bored of those quest.

You're suppose to get the rewards after doing so many of them, like trophies. But nothing in the guide says where to get or why you find those same trophies in the quest. But after say 100 or so odd jobs your suppose to get all of them, but I haven't done that many really. I try to squeeze them in between quest, but that strategy only gives me a few...

So far i've done 64 and quit one of those.

I would be happier with them if I could queue up about ten of them at a time. They're far too easy and involve too much trekking back into the guild to turn them in and get more. That just makes it tedious to try and do enough to cover all the cities.

I did them until I unlocked the city influence quests, then I stopped.

Around 100

I only did about 5.

I found those poxy little jobs tedious, so left them... too much of a grind.

Thieves quests are utterly boring and not-well-conceived compared to Oblivions, as are the other Guild quests in Skyrim (DB comes to mind). It's game development and design going backwards imo. I think Bethesda was counting on the Radiant quest system doing the bulk of the work for them, which was a big mistake.

To become leader of a Guild, I expect at least twenty in-depth hand written quests which range in complexity, difficulty and length to get there. Not some crappy 'go there, steal this, bring it back for a reward' nonsense.

Dark Brotherhood quests were very slightly different, 'Go there, kill this, come back here for reward."

The radiant quest system can be useful in certain situations, but I really hope Bethesda keeps the thing out of the Guilds in future.