I don't think so, no. when there's a storm it's just pleasantly cool for one night then goes back to being hot again. At the most maybe a light cardi or felpa if you're going to be visiting Valtellina.
I'm the opposite to you, an inveterate underpacker, probably as a reaction to my Mum's fetish for packing more suitcases than we have hands to carry them, and invariably I end up having to buy something fundamental I've forgotten, like underwear. I can travel with hand luggage only for me and DD, whereas DP likes his big suitcases, even if they're half empty. I suppose you could read a lot of male psychology in that.....
Rosa, you're making the Cornish climate sound not very appealing. Mind you, the mizzle you describe is still better than East Anglian direct-from-Siberia force 10 gales that sometimes surprise us in July. It makes me laugh when I read about people paying to holiday in Norfolk, I just can't see it as a desirable holiday destination after many years of longing to escape. How are you going to get your parts back to Venice? Smuggle them in your suitcase? Are they very voluminous?