Ive done a few quests now where the item I was meant to find and return has been tasty to say the least. The most recent one is a weapon and well, I really want to keep it as purely stats wise its about 2 times better than anything else i own or have seen.
My question is apart from having the quest stuck in your current quests part of your journal are there any other issues with not completing quests and just keeping and using quest items?
keeping quest items
I've done the very same thing for some time and didn't have any problems so far - as it seems quests are not time-bound. So basically I kept an item until I found an upgrade and then went to finish the quest 
One thing that might bug you though is that if the quest is part of a series (for instance the Dark Brotherhood or the Thieves Guild) you won't be able to advance in this questseries and thus in your ranking within the guild until you finish that quest. As long as that's not a problem just use the item and hand in the quest when you feel like it
One thing that might bug you though is that if the quest is part of a series (for instance the Dark Brotherhood or the Thieves Guild) you won't be able to advance in this questseries and thus in your ranking within the guild until you finish that quest. As long as that's not a problem just use the item and hand in the quest when you feel like it