What's your sweet indulgence? Everybody has some area where they appreciate the difference between a great product and a run-of-the-mill product, and they appreciate it enough to pay a premium for that difference. For some people, it's hi fi (8)). For others, it's food. For some, it's clothing. Where do you really appreciate the difference between so-so and great, and why?
I have a few -
The obvious - I like stereo gear. A good hifi can come close to reproducing (in three dimensions) a live musical performance in your home. Music has been around for most, if not all, of human history and it's my mood altering substance. Music done right can inspire, sooth, induce excitement or serenity.
I also like to cook, and the better tools make a huge difference. Pans that heat evenly, and retain their heat throughout the process, is the difference between meat beautifully seared and meat that's barely worth eating. Good knives reduce the amount of work, produce more consistent results and are more safe.
In my 'not quite there, yet,' category - espresso. I have a crappy espresso machine that I use every day, but I've been pining for a good one... espresso is made by forcing hot water through the coffee grounds. To be done well, the pressure and temperature need to be consistent. Most of the inexpensive espresso machines use a boiler to create both the heat and pressure (steam), but they're inconsistent in both, producing results that many espresso aficionados don't even consider 'espresso.' Good machines use the heating element to get the water to the right temp, but rely on a pump (mechanical or human powered) to provide the right, consistent pressure... Good espresso is creamy, complex, not at all bitter, and oh-so-enjoyable... but I'm still trying to justify the price of these machines...
...not that there's anything wrong with that.