BTW, I also have this discussion on GameFAQs, but I want it here, also.
I have recently created a new Argonian thief/assassin, and he has recently become Guildmaster of the Thieves' Guild.
However, I thought about not even starting No Stone Unturned, because I once did that quest during a Victor Zsasz RP, and he became obscenely wealthy (so much so it turned into a gamebreaker.)
My Argonian "Efficiency Expert" (he searches for the most efficient way to get kills without being spotted; his Nightingale Bow and his being Agent of Subterfuge have become his best friends) has become Guildmaster of the Thieves' Guild (and he is level 24); he is just about to enter the Dark Brotherhood.
I believe when my Zsasz RP began No Stone Unturned, he was about the same level, and I prefer to keep my "Efficiency Expert" hungry (it will help keep his skills up, BTW.)
And before you ask, no, the dragons are not yet even involved.
I never do that quest since the only faction I hate more than the Thieves Guild is the Dawnguard. And I still end up extremely wealthy, so a few extra gems won't really make much of a difference. And if you do have a lot of money to burn just spend it all on buying Grand Soul gems to give as gifts to followers. I do it the other way around though, I use my money to buy a bunch of Black Soul gems and give followers souls as gifts to my soul gems. Then I name a weapon after them and place them on display >:)
Buuuut... I've been told I'm a borderline sociopath.
It really depends. Just look at your previous characters;
If most of your characters reach level 60, or if at least the passive ones (with more thievery, exploration, than fighting) do reach that level, it's worth it.
Problem is that by simply levelling speech a bit, or by making some expensive potions, you can earn just as much.
Is the only reason to do No Stone Unturned for the money?
To be honest, you can get loads of dosh from all sorts of places in Skyrim, certainly to the point where it isn't an issue. The point about No Stone Unturned isn't money IMO, but the sense of 'completion' that you get from traipsing all over Skyrim finding the gems, some of which are fiendishly hard to find without spoilers
I must admit I've never completed it, even though I've tried. Usually I miss one, and can't be bothered going all the way back to find it!
I quite enjoy incorporating it into my thief playthroughs. Do a Thieves Guild quest, then take on some adventuring on the side and grab a couple of those Unusual Gems. I found it a nice way to add a little variety to my thief characters.
It's true that Prowler's Profit nets you a TON of jewels; however, I have rarely completed No Stone Unturned until well past level 20 or so, and for a thief, money really isn't that much of an issue by then. Still, there is a sense of accomplishment, and you can always choose to dump all the jewels you find in a secret room and watch them quickly pile up (or use them as "bullets" with Telekinesis... it sounds weird, but is a lot of fun xD).
I used it for role-playing reasons when playing Teccam's Crystallurgist build, tweaked slightly to allow for Smithing! I never forged a single item (other than for Hearthfire) that didn't have a gemstone in it while training to reach my glass armor. And yeah, it took me a really long time to get all those gems...