You are definitely NBU. I'm from somewhere near Ariesgirl by the sound of it, and like her I can't even imagine being able to buy a house near my family.
Dead right that many second home owners will stock up on Waitrose stuff before they go away for the weekend, because they only have frightful Tesco at their destination. They might pick up a darling little pot of chutney or something while they're there but that's not exactly propping up the local economy.
If second home owners cared as much as they claim to for the places they have their second homes, they would pay the full council tax gladly, for the benefit of the community. Especially given that many do hope to retire to that community - you would think they would want to ensure there was still a community left there when they retired.
And for the record, second home owners' absence for most of the year does not save the council money. It actually damages local communities by creating e.g. streets with no occupants, no lights on at night, schools closing because the families with kids have had to move away, bus services being reduced because the second home owners are not going to catch the bus in a million years etc.