If you have noise, this is a different situation. You need to determine the noise source. It could be harmless, or it could indeed need some attention to the chain or related components. My comments regarding timing chain replacement relate to an engine that sounds good, runs good and is properly maintained. Whenever there is noise it should be investigated. You are doing the right thing seeking information. The best approach would probably be the helpful ear of someone experienced with these engines. We just can't diagnose noises over a discussion forum.
Chain wear resulting in 10 degrees of chain stretch is SIGNIFICANT. Typically, at least in the inline MB engines that I am familiar with, five degrees of "stretch" warrants chain replacement, but may not display noticeable performance or fuel mileage degradation. But, yes, ten degrees would probably result in noticable performance and fuel mileage changes in an engine. Ten degree "stretch" in any engine would warrant, or even DEMAND, chain replacement in my way of thinking.
Yes indeed things expand with heat, but they also contract when cooled again. "Stretch" of a timing chain is due to one thing, wear of the pins and bushings. Infrequent oil changes allow build up of microscopic particulate matter that accelerate this wear. In the case of a drive chain, the term "stretch" is misleading. The chain "lengthens" due to the wear of the individual links.
Your list of items which would cause chain noise is good information, except the chain, at least in an MB, could probably not wear beyond a point where the tensioner can maintain tension. If the chain and components are this worn, the engine has probably never seen an oil change. This would probably be a completely worn out engine that is about to "let go" any minute.
Have a great day,