I had an SP for many years and got a VP replacement. 4 heads on the VP but 2 on the SP. With the SP no matter how well you set up the printer, there is always slight banding. The print heads (Epson dx4) are 2 channel (2 separate colors). The SP shares the heads with different ink colours in the same head. Blue and black in one head, red and yellow in the other. This sharing can cause some problems. Sometimes the ink would contaminate themselves, the red goes back into the yellow. The VP has a head for each colour which eliminates the contamination problem, banding problems and doubles the printing speed. The SP is a workhorse, but if you can get the VP it would be a good upgrade. But if I was spending $8K I would spend more and get a new print only machine, then buy a separate cutter. I might even check out HP.
You need to see the hours of use these used machines have on them. This information is stored in the printer and you should get them to print this info off the machine in your presence. The printer stores the headshots/ use of the heads, headstrikes (bad) and lots of other info. I would also buy a roll of 54" vinyl and print 20' long prints of images that will show issues. High res photos, plus large areas of solid colours. Same with the cutter. Run print cut jobs to check the alignment. DO NOT buy a unit that has issues with promises of getting it fixed AFTER you own it. It may never get fixed once they have your cash. These are huge purchases and you could get screwed. Be very very critical and suspicious. Think of the printer salesmen as used car salesmen. Don't trust or believe them.