Simon, I think that the comparison could work, but only for a few instruments. For example, we could easily compare acoustic guitars; comparing saxophones could be a bit trickier: are we talking tenor saxophones softly blowing a ballad or honking away a rhytm and blues solo?
I think that the most difficult thing of all would be to compare strings: most of times these are used to play a background pad, but how do you compare two pads? It's too subjective...
Maybe it would be better to narrow the comparison to solo instruments with a well defined personality (e.g., speaking of strings, a solo violin or a cello)
Hmmm?