I have owned both.
VP is almost twice as fast due to 4 heads. It has both channels in each head the same colour so no chance of the yellow sucking up red like the SP.
VP has "variable wave technology" to help eliminate banding. I am not sure if that's why, but it prints with zero banding. My SP always had traces of banding even when perfectly calibrated.
VP has lower stand so you can reach the front when loading media. The taller SP gives ink a little more time to dry before it reaches the floor or my Supply55 take up reel.
VP way easier calibration test. It print a bunch of squares on squares and you pick the best one. The SP prints 1, look at it, punch in setting, print another, look at it, punch in setting, look at it, punch in setting...
VP has inks out back making it shorter especially when using 440cc cartridges. It makes it a little more cumbersome behind because of the inks sticking out the back of the VP.
VP has belt and no cable. Cables stretch.
VP has the encoder strip somewhat protected from the over spray the heads produce when printing.
VP does automatic enviromatch every time it checks the media width. SP enviromatch is manual routine.
VP spits ink into caps when printing, SP has felts it spits into that cause misting and require replacing.
VP's much tighter to work on. way smaller opening for cleaning heads. Tighter space in back to load vinyl.
VP keypad has eliminated a few function specific buttons. No big deal but takes a little time to adjust to it. The actual functions are the same, the VP has some extra functions.
VP has a function that tracks rolls, and the amount of media used off roll, and prints this on the end of roll. You manually enter new roll into VP first, and tell it when using that roll.
VP not as robust, frame bottom crossbar folded metal not solid tube like SP.
There are other differences... can't remember them all.
In conclusion the VP is not as heavily built as the SP. They apparently have the same structural support across the bottom, and the VP is a much faster, better printer. I cannot say if the VP will last the 10+ years and counting people are getting out of the SP, but the VP is better.