In my recently rotation in radiology (on month), I must have seen 15 or 20 of these variations in the lumbar area. There were several with six standard lumbar, several with transitional lumbosacral bodies (always seemed to be a judgment whether to call them lumbar transitional with sacralization or sacral transitional with lumbarization, the former seemed to be more preferred though), a few thoracolumbar transitionals (vestigial ribs, labeled as thoracic pretty consistently I believe), and a few that were tough to even categorize.
I don't recall there being a tremendous increase in spondylosis for these patients vs "normal" anatomy, but then obviously if you're looking only at the subset of the population that needed a lumbar plain film or CT then that isn't exactly representative. I didn't keep a list though, so perhaps there were some degenerative changes at earlier ages than would otherwise be expected?
The biggest concern, from what I observed, was more in how to label and number them so that reports were consistent from one physician to another and across time, especially considering different imaging modalities used may have shown the transitional elements more or less clearly, or cropped one end or the other of the lumbar area making it difficult to count with confidence. I did see one case of low conus and fatty filum where there was an extra lumbar body, and this created a bit of uncertainty of whether the findings were suggestive of tethered cord due to the positional anatomy variation.
