I would not reuse the columns. Yes, most of the DNA has been eluted, but it's not 100%. I have run a second elution if I needed more DNA and gotten DNA off the column.
I suppose, if I were doing several minipreps of the same sample, I might reuse the column, but it's not worth my time to run multiple preps sequentially when I can do them all at the same time.
You also have to worry about DNAses and other contaminating proteins which should mostly have gone away in the lysate precipitation and column washes, but you can never be sure, and is it worth possibly contaminating two samples?