From what you said, it appears to be an unfinished area of sub basement. Not a finished laundry room and tool room. So, then Mark is correct, it would not add value. However, if it were to be completed that would be a different story.
Sounds like you are describing a quad level home. There are very few of them. Depending on the condition the sub basement is in, that will determine the value added, or taken away.
You can ask the realtor that showed you the home. Or, please feel free to contact me directly. But ask for comps for a quad level home. Not a Ranch with a basment and a sub basement. The values will be different. Hope that helps!