For Me, I would take more space any day. You can add more light easily, you can't add more space to that bedroom. I wish we had a basement. My sewing room (bedroom) is very small. I'm always piled up and can't find my things due to lack of space. FYI- You can now buy the new energy saving bulbs ( curly Q bulbs) in a "daylight". It has a more white light color, not that orange or yellow cast that so many have. If you have a Home Depot check out the light bulb section and they have a display with 4 different bulbs and if you take a look at that you can tell a BIG difference in the colors they put off. I was amazed at what I saw. I was trying to choose a new color to paint our bedroom and everything I tried on the walls looked orangeish yellow. Changed the light bulb to a daylight one and got a more true color. Amazing.
Oh, and buy the way paint or decorate in light bright colors. They say no lavenders or purples, they are supposed to be depressing. I don't agree, just what THEY (whoever they are ) say. Have fun with it and have a great time if you decide to move you sewing room.