In my area, there are a variety of split level floorplans. Many have grade level rooms such as a family room, extra bedroom/office or maybe powder room or laundry. There are splits that have, in addition to the grade level room, a below grade basement, as well. It may be a full or partial basement, and it may be finished or not.
There is more value, here , with a split that has that basement - preferably a full basement. The additional storage space is valued...and the potential for finishing it off in the future, adds more value.
I don't know if the lower level you are describing is similar to the grade level layout I described...or if it is considered to be a grade level basement, without defined rooms..
If you are trying to figure out the value of your home, you need to look at comparable homes (other split level homes in the neighborhood) that have sold recently. That is really the only way to get a good idea of what your house will sell for in today's market. Let me know if you would like to meet to discuss your home's value.