I've tried the mindfulness steps you mentioned too. I just can't seem to turn off the noise in my head. Believe me there are times I really wish I could.
I do find that when I do "step away" from all the distractions and such, I usually come back with the answer to whatever problem was plaguing me a the time, usually coding related etc. I have a lot of the "Eureka" moments, I love having an Epiphany, but as far as "focus on the here and now" I have a really really hard time doing.
You cannot turn off your head. But you can make it a bit calmer.
And I also experience what you say about the eureka moments.