Found the answer by reading through archived forum pages. On a Mac, just use the "Accessibility" function in System Preferences, to activate keyboard zoom. "Command/Option +" will then enlarge the entire screen, thus making v-synths appear larger. A little crude, but it works! Not very satisfying, however, because my mouse will drag the entire page up/down by a few centimetres every time I place the pointer near the top/bottom/edge of the page. I understand Arturia may someday build a GUI adjustment into the v-synths, but for now I guess this is all we can do.