Okay, I think I phrased my comment wrong so I'll try and explain myself better.
I was only suggesting to avoid downtown Cagliari those days (my main concern was the 30th, actually) because it will be in sort-of lockdown as it's the day before the parade, so getting around is going to already be hard for residents, let alone tourists. Besides, many of the tourist-y spots are in the same area the parade will be held, so unless they plan out beforehand what else to visit on the 30th in the city (which is possible), that day would basically go to waste. Not to mention, the security will probably be tightened this year on after what happened in Turin in June, and it's likely that fewer people will be able to watch the parade as a result. Nothing has been decided yet, though. I don't think it's the best countermeasure.
Don't get me wrong, if OP is actually willing to get up very early to find a decent spot then stand under the sun for a couple hours waiting for Sant'Efisi to arrive, by all means, they should absolutely do it. It's a great experience and a great way to see the diversity of Sardinian traditional costumes and a piece of Sardinian culture.