I'd say "go for it". Having a small space upstairs sounds like it would help you with your creative side to sew a bit now and then. But also, adding more good lighting downstairs will help, and perhaps you will be more apt to go down there for extended times of sewing.
Hope you come up with something that works well for you!

If you want to keep the basement space hang up more lighting. In my last house I was in the basement and I bought work lights from Menards. They were about 12$ each plus the cost of fluorescent bulbs. I used the daylight bulbs. They hang from the ceiling by chains. Not fancy but that room was sure bright.

When I bought this house I thought the basement would be the perfect spot and size I'd need. Little did I know I would continue to add to it to the point its no longer large enough to hold all "MY STUFF". Anyway, since I had to change out the fuse box to a breaker box I had the electrician add more plugs along the walls and shop lights on the ceiling. I had a general idea where I'd put each machine at the time so knew where to add the lighting. So far its been working out great for me. Now my sister just bought a house and is adding lighting in her basement and she's having these new LED shop type lights installed. Pricey but nice looking and a lot of light to them. So I'll replace mine when they start to go out on me. Wish I knew about these new LED lights beforehand as I just had to replace the ballast on one of my lights recently.

I also have a big bedroom set up for sewing and have my longarm there...but lately have brought out my FW and am working in the living area, don't like to be too much out of the "action". Even if it is just DH and I, kids stop by sometimes. I will move back to sewing area after I finish this project because Thanksgiving is coming and need the space.