Ask your husband to reverse while you stand watching how close the curb gets. I have to admit I completely understand my husbands' frustration with women drivers, we both rage together sometimes ha
Seriously ? 
say you're trying to get out of a tight parking spot as people have parallel parked both in front and behind you tightly and you're going back and forth while steering to try and get out - how can you gauge how far away the front bumper of the car behind you is?
That really is a case of getting used to how long your car is. When you change cars, it is different. (Unless you have parking sensors I suppose - don't know, I've never had a car with them).
I assume when you guys advise moving the mirror down, you primarily mean this would help if the kerb was to the right or left of the car right? I feel like it wouldn't help visibility to see the kerb directly behind my car?
But I can't envisage a situation where you would be reversing, towards a kerb, that is narrower than the width of your car, without any other thing (hedge / wall / signpost / lamp post / etc) behind it. If there were every that scenario, then it wouldn't matter if you inched back until your wheels touched the kerb. Your boot would just be overhanging 'space' so it wouldn't be an issue.
Where - above - you've described reversing out of a parking space and there is a kerb around a tree, then surely you are turning your wheel (either left or right), so, therefore the kerb would appear in your wing mirror as you turn.