The thing is, in a sense, you do 'lose' a bit with a win. By putting up $120, you should really be winning $109.09 (assuming a -110 money line) instead of $100. The half point will not save you enough times to make it worth it. If it did, the books would not offer it. If you think results are hitting close to the posted lines, you might be better off pursuing middles.
Never buy points in the NBA...unless you want to give the house a bigger edge.