I've always been sceptical of this kind of theory, where you can improve real-life skills in dreams, mainly because it is extremely hard to have a non-egotistical state of mind while within a lucid dream. For example, you brought up hand-to-hand combat. In real life, I have a realtively low chance of winning a fight, because I have no formal training in unarmed martial arts or anything. However, in a dream I always picture myself as a total badass with a zero percent chance of getting scratched. I realize that this kind of thinking can be reversed as you mentioned, but creating a scenario in which a dream character has more skill than you at something is in my opinion impossible. How can you create a realistic entity with your mind who has more knowledge about something than your own mind does? It doesn't make sense to me, but if you can find a way more power to ya.

Now, what might be possible is practicing at independant or passive activities in a lucid dream. For example, if you had a concert or something coming up and you needed to practice your jazz trumpet solo, I think it's absolutely reasonable to be able to emulate a fully functional trumpet and play it in a similar if not identical manner as in real life. Assuming you have a solid understanding of the required key combinations and embouchure to play each note, as well as what should happen when unintended notes are accidentaly played, there is no reason you couldn't practice and experiment while dreaming.

It seems like anti-dream control to me, in a way. Like normally you try to bend the dream to your own will, but here you would be bending the dream to fit the laws and causal nature of the real world. Weird stuff. I might give it a try sometime.

But anyway, that's just my two cents. Don't let anyone else's opinion influence your thinking too much; remember that the dream is what you want it to be, not what I think it should be!

Keep us informed on your findings!