Sometimes people wonder why we keep around all that "old" data when there's newer and higher-quality data available of the same targets. Like Viking Orbiter and Mariner 9 images--MGS beats the pants off that old data. But you're right about historical continuity, for one thing--you can check the old Viking & Mariner data against new MGS images to look for changes over time. And with modern image processing techniques you can clean up the old data quite a bit. I've found it useful from time to time to find old Viking medium-resolution images to provide the context for extremely-narrow field-of-view MGS/MOC images.

now if someone would only define the standard white values.

In the course of researching color theory to back up my MER software, I learned that there a number of standards called "illuminants" that define various standard "white" spectra. There's D65 which is the spectrum of natural sunlight on Earth, D50 defining the spectrum of a tungsten filament lightbulb, illuminants for flourescent lights, and on and on. It struck me that Dr. Maki missed a bet in his paper by defining only an average color for sunlight on Mars. He could have defined a Mars illuminant, "M65", which image processing software could use as a reference for color calibration. As it is, I have to use Earth-based D65 by default plus ground-based filter calibration, and trust that I'm in the ballpark and that the contribution of light filtered through the Martian atmosphere is being accurately represented by filter calibration alone.

As for coordinate systems, there's been an ongoing effort for decades to develop and refine coordinate systems for all the planets. USGS is the official keeper of the standards, and they've defined reference latitude and longitude systems for all the hard-surface planets and a lot of moons. Their big challenge is that their data is based on really remote sensing, and so the coordinate systems are a moving target. The system for Mars keeps getting refined based on new measurements of oblateness and elevation, and so now there's a problem translating the coordinates stored with old archived data to new systems. There's about a kilometer difference in longitude "calibration" between the coordinates stored with Viking Orbiter images and the coordinate system being used to archive MGS data. Tower of Babel...thank god we have computers to do the translating for us!