Things I didn't think I needed, but now LOVE:

Kitchenaid Ice Cream attachment. We're really happy with the results and I like the idea of using a single appliance in multiple ways. Only hassle is remembering to put the bowl in the freezer several days before you're ready to churn.

Ditto on Kitchenaid meat grinder. Use it all the time, and not only for meat - my mother has an amazing gelatin recipe where you mostly use ground up entire oranges and apples. 2 minutes work with the Kitchenaid.

Kitchen scales. Now that I have one I use it all the time, especially for things where the recipe calls for something impossible to measure, like 2 cups bread cubes, but also gives the amount in ounces/grams.

Slow cooker. I remember when they were called "crock pots" and looked stupid, wouldn't have one in my house. The new cookers are amazing and do some things better than I could possibly do any other way. We have a recipe for slow cooked pork shoulder for pulled pork, perfection in the slow cooker.

Panini maker. Use it all the time for many things including open faced toasties, but also for things like reheating pizza.

Egg cooker. We've had this discussion before. I know how to boil an egg, but with the cooker I can just put them in and forget about them until the buzzer goes off, and they're perfect every time.

Silicone baking mats.

Hand cranked pasta machine. Ignoring the resting time, it takes less time to make and cook the pasta than it does to start with the dried stuff.

High quality metal measuring cups and spoons.

Now, what I really want is a wood-fired pizza oven, but I think the condo board would object.

Mistakes from the past:

Hand operated nut chopper thing - hard to use and bad results.

Kitchenaid pasta extruder. Hard to use and not good results.

Fancy corkscrews. In the time it takes to get the rabbit set up I can just grab old faithful.