I read your post.  My microwave is 30+ years old, so I didn't think a post by me would be relevant.
After reading on how long (or short) some others have kept their microwave, I wonder how long mine will hold up.  As long as it works......  I'm keeping it.

My microwave is made by Panasonic (I think).  I looked and Panasonic makes commercial grade microwaves. I wondered if that would be an option...... then I looked at the price.

Probably a good idea would be to go to manufacturers websites, look at models, and maybe buy direct - or at least by from an appliance dealer, as opposed to buying from a big box store. Just a thought.

Good thought on looking at the warranty. However, if you read complaints on microwaves, most times it seems the things that go wrong are not related to the cooking side - door latches that break, etc.  Something to pay attention to.

Just some of my thoughts.