As I said, it’s all a matter of willpower. If you believe you won’t feel pain, if you KNOW it, since it’s a dream, you can do it. The same for fire powers/rubber body/invincibility/whatever. However, while you don’t have the willpower/skill, you can make use of “shortcuts”, like the famous lucid pill, or as you said a special belt. That works too.
You are right. Plus, with acronyms like that the LD4All forums have a fancy explanation if you put your mouse pointer over them.
I’m not completely sure about this, but I believe that you can perfect techniques and get better on doing some stuff. Since you’re in your mind, they say it’s a good way to get ideas, since you are thinking “right from the source” 
It’s good for your creativity, apparently. (check this post for example on learning stuff: Here)
If you consider a spirtism approach, you could learn stuff from other spirits or remember stuff from past lives 
EDIT: Also, as Asmoudeus said, you can learn a lot about yourself. People use SGs to learn about themselves, get questions answered, etc.
(a quick note on the SG thing, if they are really spirits or not, there’s a discussion I think that would be interesting for you to check if you had questions: Here)
Good thing that you remember at least a bit. I suggest that you write it down, and keep a journal IRL or in the forums, like me. Another good thing to do is keep a notepad or something next to your bed, so you can write down your dreams as soon as you woke up so you won’t forget anything.
Those flashbacks that seem real are called False Memories. You get a lot of those in dreams, you’ll get used to it
Good luck on dreaming and LDing.