should I rework this 3/4" main water line into 1/2" branch circuits?
@ Roberto, I would change the water line to exactly what you show in your bottom picture. In my home there are no 1/2X1/2X1/2" tees. All the 1/2" lines are teed off the 3/4" line and when one device uses water, say someone flushes a toilet, the person in the shower does not see a reduction of water flow or a major temperature change in the shower water. There have been many posts where people ask "how do I keep adequate water flow when I have 1/2" plumbing", Your drawing is the answer. This works for me.