Firstly, auscultate =\= oscillate.
Do you not consider lung sounds an absolutely vital part of the practice of medicine? I listen to lung sounds on almost every patient I assess as part of a basic physical examination. In my opinion, it's fundamentally important. They help guide my initial treatment decisions, assist in trending their efficacy, and diagnose problems in some cases. Waveform capnography, pulse oximetry, and the remainder of a physical exam also help out here, but LS are a huge piece.
I don't auscultate blood pressures all the time as I use the NIBP function of my monitor more frequently, but proficiency in manual blood pressures is also pretty integral to EMS, particularly as a BLS provider who likely doesn't have an automated option available.
I am far from an expert on heart tones, but I still like to listen to them. My understanding is that modern diagnostic tools in hospital have greatly decreased their historical importance, but it's interesting to piece together known pathologies with unusual heart sounds.
I don't carry my stethoscope around on my neck when not on a call. It's kept in the back seat of my unit in my personal gear bag. When I arrive on scene of a call, I take it out and place it around my neck. I use it on that call, then clean it and put it back in my bag. Sure, some people use it as a symbol, but I'd get annoyed with it around my neck all day. You don't have to use an expensive cardiology stethoscope, but I've found it worth the money to get one that's comfortable, doesn't have rubbing sounds from the tubing, and transmits sounds loud enough for me to hear them clearly.
What's wrong with people using it to express their personal tastes a bit too? No one is disputing that funky colors and finishes are "necessary", but some believe if you have a tool you may as well personalize it. To each their own!