MS doesn't really 'travel' in that sense. Lesions (areas of present inflammation) and scleroses (areas with evidence of past inflammation) can appear anywhere in the central nervous system (the brain, the spinal cord, the optic nerves) with no real predictable pattern (aside from some areas of the brain being more 'typical' for MS lesions than other areas of the brain).
However, spinal cord lesions *can* be a bit trickier. If a lesion appears in the brain, it may very well produce no symptoms at all. Because the spinal cord is such a smaller/narrower area than the brain with less tissue around it, a spinal lesion may be a bit more likely to produce noticeable symptoms.
But as with everything with MS, its course will be highly, highly individual. Someone may have a lot of symptomatic difficulty with zero spinal lesions while someone may have spinal lesions with minimal symptomatic complications. It's truly impossible to predict.
If someone has spinal lesions, it's neither 'minor' nor 'serious' when stated with no other context. It is just their personal manifestation of MS as found by exam or MRI. You'll find folks here with spinal lesions and without them (that they know of. They can be tricky little devils to image properly!), and every flavour of symptoms (including none) among them.
I notice this is your first post. There's a lot of information here and it can be a bit overwhelming to start with. But I'd like to point you to our health pages. There's a wealth of great info over there.
http://www.medhelp.org/health_pages/list?cid=36
This one may be especially helpful as it deal with spinal lesions directly.
http://www.medhelp.org/health_pages/Multiple-Sclerosis/Spinal-Cord-Lesions/show/764?cid=36