I think you are on the right track; Kevin does a fabulous job with his rum reviews.
I would consider taking a course. A few years ago, I took the BarSmarts series of online courses (and exam). There was a large portion of the course on learning to taste spirits that I found extremely useful. It's also very helpful to read about the production methods of the different spirits, and all the information about what can influence their taste. Also try attending spirits tastings in your area, often bars have them and it's a good way to educate yourself about a certain product, especially when the people who conceived them, distilled them, etc, are the ones doing the presentation.
I think it's also important to keep in mind that different criteria apply to spirits that you intend to enjoy neat, or the ones you intend to mix with. I've tasted spectacular rums that completely got lost in cocktails.
About Appleton VX vs 12, they are both very good. You've tried both of them neat, maybe try mixing the same drink side by side with both, and see if you have a different perception. Have fun with it! And maybe revisit in a few months/years to see if your taste has changed.