I would give a machine to someone who needed one and could't afford to spend much at the moment. I feel much better about it when I know the receiver cares for the machine. I probably only need one sewing machine, but I have three I use regularly and will not part with any of them unless I had to.
At the moment I dont' know anyone who would consider a vintage machine. I would first try and sell a machine I have fix up and assume it will go to someone who wanted one. I have 5 machines, one I might sell and one who needs a bit of work. I have my eyes on a Gritzner long bobbin, and it's mostly for its' nice decals. A machine in reasonably working order leaves the local charity whitin a couple of weeks, some in just a few days. If I take it there I know someone will buy it; but I suspect very little actually goes to charity. After a couple of weeks they tend to lower the price.