I currently own a Spyder3 along with an NEC PA271W and SpectraView II software.
The PA series displays are individually measured by the manufacturer. This is accessible without a measuring device of your own, using NEC MultiProfiler which is a free download. That's what I use. I don't even bother with measuring the display anymore. You choose the settings you want, the software interpolates based on data in your particular display, and then uploads a calibration LUT to achieve the results you want, and also builds an ICC display profile.
But I'm curious if there is any value moving to the Spyder4 given its specification towards wide gamut monitors. Has anyone tested for noticeable differences/improvements? Is it worth the change?
Not for this display. What's unclear, to me, over the long term is how well backlight decay is compensated for by the firmware/software method of calibration. I would only consider the mdsvsensor2 or 3, which contain a custom calibration matrix for the primaries used by NEC displays. Or use a spectroradiometer.