Skyrim : Should i keep the Goldenglow estate deed?

No. Keep doing the rest of the thieves guild quest. after they send you on another quest to see this argonian named Gulum-Ei or something like that, and he has the actual goldenglow estate deed, which he gives to you for sparing his life, You can then bring the goldenglow estate deed to maven black-briar, and she'll pay you/the guild for it.

There's no benefit to keeping it. There are no other related quests and it gives you nothing to keep it. Based on conversations with Maven Black-Briar, it seems like there was supposed to be a quest where you could give it to her for a presumed award but once you have the deed, there's no option to give it to her. It has no value and you don't get to act as owner or anything.

Edit: You do have to keep it in your inventory until after you've spoken to Brynjolf, Maven, and Mercer so for awhile I believe it's stuck in your inventory until you reach a certain point in the questline. Once that's complete, it becomes sellable/dropable and at that point it no longer has any purpose.

Yup