If you feel it makes no difference, return it.
SP is really just for cleaning superficial dirt on used LP's. It will remove some skips/stitches depending on the degree of damage. Otherwise, it won't perform miracles.
Mine has been in use for over 10 years while I keep saying "I'll get a US this year"
US is the answer if you want to hear a difference.
Get the Humminguru or equivalent for cheap.