Using the comma as a list of things vs two related thoughts

Recently I sent a mail wishing a friend well. I ended it with the following sentence.

Please take care, and call me if you need anything.

The comma was included because the two were separate thoughts with the latter as an add-on to the former. Consider it without the comma.

Please take care and call me if you need anything.

While grammatically correct, it sounds like a to-do list--please do the following things: (1) Take care, (2) Call me if you need anything.

Would you agree? I see this cropping up in a lot of writing here and there.

I phoned my wife, and slept for 2 hours

seems to be a description of the list of things I did this afternoon, while

I phoned my wife and slept for 2 hours

sounds like I'm reporting a very boring conversation.

Structurally, there are two different ways to write things.

I phoned my wife and slept for two hours

lists the two activities done in the form of A and B, while

I phoned my wife, and I slept for two hours

joins two related complete sentences using an optional joining comma and and so that we do not write them separately.

I would not write

*I phoned my wife, and slept for two hours.

I don't think the use of the joining comma (R L Trask's term) need ever create ambiguity which cannot be resolved by the context.