Ducati Voltage Regulator fuse

Visually checking for a spark is OK as long as you feel very comfortable that one or more of the other cylinders are not going to fire.
In your case, cranking gets you No results, so OK!

Crank the choked engine for 10 seconds before pulling a bottom plug and observe if the plug is wet/damp and/or smells of fuel.

My new capacitor was wired in with the correct polarity and the voltage regulator fuse is not being blown.  This issue appears to be resolved.  Because my engine starting and rough running seems to be an unrelated issue I've split that off into a different forum topic and added some more detail of my investigations to date.