You do not note what type of spondylolisthesis you have (isthmic vs. degenerative-see website) and normally the L5-S1 level is an isthmic slip. However, ganglion cysts are associated with a degenerative slip so I will assume this is a degenerative spondylolisthesis.
If you have leg pain and lower back pain along with losing “30% of the feeling in my legs”, I would assume you would be a good surgical candidate. See the section “when to have lower back surgery” to understand this concept.
“Minimally invasive” spine surgery is a misnomer and a marketing ploy. 50% of the spine surgeries I do are revision surgeries (surgery to repair a pervious failed spine surgery) and most of these are repair of “minimally invasive” surgeries.
Find a well experienced spine surgeon who is meticulous and you should be happy. You can read the section “Questions to ask your spine surgeon”.