You might want to consider how someone that designs a passive implements it and don't underestimate what the "switch" adds to the mix. For example, in a resistor-based passive you can have shunt, ladder, or series type attenuators. You might also just have a "pot" in the box. A simple attenuator with a wiper. Magnetic passives can use transformers or autoformers, and there is a difference in how these work and why one might be a benefit over the other. I also don't agree that a TVC imparts a warm sound. Any passive I have had or built, and there have been many, has been very transparent.
That being said a good yet simple LDR design that still makes the rounds in my system is the Lightspeed Attenuator. Don't let the price or looks fool you. It's an amazing passive if all you need is one input. The benefit of a light dependent resistor is it takes the switch out ouf the equation. I have had passives with Seiden, Shallco, Khozmo, Elma, and other switches, as well as NOS Noble potentiometers, and a simple well designed LDR is clearly different and shouldn't be overlooked if you are serious about going down this path.