Is it a good idea to convert a little used family room into a bedroom?

We have a split level house, 1,700 sf, 2 bedroom, 2.5 bath. The garage is on the lower level along with the laundry room, a small bedroom, a full bathroom & a family room.

The upper level has a decent sized open concept living room, kitchen & 2 dining areas as well as a half bath with linen closet and a huge master bedroom with full bath and walk in closet.

We have lived her a year and have never used the lower level family room. It would be very easy to frame out a door and closet to make it a third bedroom. I would still furnish it as a den to give potential buyers the idea that it could be used at either.

I estimate the cost to be no more than $3,000, including labor. My question is, would this add value to the home if we were able to list it as a 3 bedroom, or would it not affect the value vs a 2 bedroom with living and family rooms?