OK, I like this. BTW, I'm assuming that Row above is similar to Values from before. Yes - Values was a dumb name.
Vector is a good idea.
I have attached one possibility below. The remaining problem, for the IDL as well as Guppi, is handling arrays of plots and overlaid plots simultaneously. Basically for each X axis, there is a sequence of Vector pairs for each Y axis. The Vector pairs are one X vector and one Y vector for each overlay. I'm only on guppi-list, but I'll check the archives.