I remodelled my spare room last year as it had just turned into a dumping ground I could close the door on. Decided it was wasted space as a spare "bed" room so removed the bed, decluttered the junk, redecorated. Now it's a multi-function room with a fold out sofa, dedicated home office space, craft/hobby table and yoga mat.
I'd love to remodel my whole downstairs and move the door going into my kitchen to create a better useable space in the lounge but that would involve moving electrics, kitchen units, a radiator and making good the supporting wall. So not as cheap/easy as it seems!