Gotcha, yah it's a BIG table, so it may be finding some edge-cases on the export options.
spec_plot() is essentially for sparkline-style plots (histogram, line plot, dot plot) or summary stats (boxplot and equivalent). So yes, only very simple plots, and actually done via SVG + base plotting as far as I know.
In theory you may be able to do something similar with ggplot2 but I haven't been able to create a clean example.