If your DP came home on a random Tuesday in July with a bunch of flowers or some wine, just to say "thanks" for everything you do for him and your children, would that be pointless too
No, it would be really nice, because Clinton Cards hadn't told him to do it because it was Mother's Day. It would be nice if it didn't have to be Mother's Day for someone to show their appreciation of their mum/other half (and same goes for Father's Day).
Yes I do think it's nice to buy someone something just because.