Gnome Stew has a great article about how to deal with situations where players will quite often latch on to a minor detail and turn it into something greater than what you, as a GM, intended. I know I’ve run into this before, myself, and while it’s sometimes hard to really fly by the seat of your pants sometimes, it’s definitely rewarding if you can find a way to turn the players’ focus on that minor element into something rewarding, even if it’s ultimately irrelevant to the overall plot.
Check out the article on Gnome Stew
Also, check out this small article about prepping for a game that I definitely agree with. It’s about saving details as you think of them and fleshing them out later. I, personally, used this method for a sandbox-style D&D campaign I ran last year that went very well.