I'd suggest it can be used even more lightly than that, to express that someone is pitiable in some way. My boss, who is from the Carolinas, was talking about her mother who had just had a stroke, and said "my momma, bless her heart".
As you say, there are shades of meaning, and context is sorry important.
Terminator 2. The ad campaign and trailers revealed what had the potential to be an amazing reversal of expectations well ahead of time. I actually got to see it with a friend who was out of touch enough to not have seen any spoilers; I wish I'd had his experience.