In the Thieves Guild, you can take up optional missions(stealing a specific item, breaking into a house, forging ledgers, etc) , I'm just wondering, is there an end to them, or are they repeatable? The people who give them, when asked about them, say that doing these small jobs will help get the guild back on it's feet, but so far, they just seem like random, pointless, repeatable quests to earn you money, are they?

Bump?

Yeah I have done a few. They are still fun and to me the way the system works for the thieves guild (imo) is that you do the thieves guild primary quest line which fulfills the story, but severely lacks in actually stealing things.

So if you actually want to be a legitimate thief you can do those infinite ( at least thus far for me) side quests or just pickpocket and loot/steal things and sell them to the various fences you can acquire throughout the quest line.

Good luck and Happy thieving !

Yep, there are 40 of them (I'd recommend the Burglary jobs, they are the fastest)
There are 4 special jobs which will earn the Thieves Guild respect in each major Hold

(Whiterun,Markhath,Windhelm and Riften)

Edit:There is an achievement for this, also you get the "Guild Masters Armor"
You get a short ceremony which makes you the leader of the Guild, officially.
The Rataway is restored, you get 4 merchants set up just outside the Flagon and the whole Guild just looks much better.