It sounds like you are doing all the right things. This is fantastic and keep it up! Although it is frustrating that only a fraction stand out, that is reality. The reason people have fantastic photos is not because they get them all the time but they are really good at culling those that aren't. The average submission to publication ratio at National Geographic is around 100:1 and these are among the top photographers who are already highly skilled.

Some people do replace the sky when they don't get a good photo that they want which is fine but it not in my opinion photography, it's a different art form. If you want to become a better photographer, keep improving your photography skills. No publication will accept photos with elements replaced (sky or not) if they are trying to depict something real. On the other hand if you want to publish a calendar (or similar) of artistic images you can pretty much do whatever you want. There was a famous series that replaced all skies with a scaled up version so that the moon would appear much larger. That is art and it has it's place.

Elia Locardi has his own unique style created by heavy layering of images. Usually he takes the same photo over and over and painstakingly blends them by hand to select which area comes from which layer. By his account, it takes him several hours to days until all the layers are blended to his liking on some photos. He has been a presenter at several photo conferences and he's a very lively speaker that shares plenty of details on how he builds his images. The best comparison is something like HDR but over time. If you pay close attention to the lighting on his images, you can distinguish some parts taken at sunrise and some at sunset in the very same image.