RE: Sardinia in May?
I'd stay in Palau. The drive is short and pleasing, plus the sight of Porto Pollo down the slope from the top of the last hill is something you will love to see each time. More, it is not said it will be windy every day, it is not said it will be always Ponente, it is not said Porto Pollo will be the best spot every day, it is not said you will want to sail each day... OTOH, of course, if you wish to be able to sail every last second of Ponente, stay in Porto Pollo and take your risk.
Don't expect much from Palau, anyhow you are right: there is something to buy and something to eat there, while Porto Pollo is probably almost desert that time of the year, expecially after the sailing is done. Only, beware of leaving your materials on top of a car at night.