My biggest mistake was the bobbin "sidewinder" that I got at Hancocks for about $19. It is too lightweight and bounces around and never produces a smooth wind, lots of lumps and bunches. I, too, do not care for the blue round sharpener. It did not work for me.
One neat thing I use all the time is in the Furniture polish-cleaning section of the store. It is made by Pledge and is a plastic thing with 2 brushes inside and the lint and junk go up into the enclosed top area. It is great to run over my cutting board before using it. The cats track onto my board, and dust collects but it cleans it all off really well before putting a blade on it. It's also great for picking up thread pieces.
One other comment about magnets. I used a heavy duty one from the auto parts store to pick up pins out of my carpet. I believe it was responsible for wiping out the brain of the sewing machine I had. From then on, I am careful not to get them too close to my machine.