Convert it for sure! I have had one of my clients with a two plus den put a closet into the "den" and now it is a bedroom. Of course, the tax records will still say two bedrooms but having that option for a 3rd bedroom is the way to go.
Three bedrooms are looked at more, sell more often than 2s. How much faster? If I could answer that with any certainty, then I would be advising kings and queens instead of kissing a lot of frogs until a prince comes along.
But with 17 sales last year under my belt, I think you can trust me to say, TURN THAT ROOM INTO A BEDROOM by simply adding a closet. If someone wants it for a den or an office, well goodie, but another bedroom is always welcomed in Florida where one ends up with more guests than envisioned.
If you have some friends who want to buy in Sarasota, I'm your gal. Please send them my way and I promise they will thank you.