I'm going to get attacked for saying this, but I think sometimes people under-estimate the Mercy of Allah swt. Here is a servant beseeching Allah for His help in matters only Allah knows and I honestly don't think Allah will not help His servant regardless of what the intention the istikhara was for. To me the mercy of Allah is unlimited and by assuming that I cannot ask Allah by istikhara what I want would be saying that I am not hopeful for His mercy. To Allah it is the intention that counts.
When my sister was killed, I did istikhara for the purpose of knowing who killed her. I saw the man responsible in my dream. He just appeared in front of me for a few seconds then vanished. SubhanAllah, I had begged Allah to give me a sign and He did, because I had faith He would.
And some may say it was the devil blah blah... but no, we found out afterwards that he was the one who did it. Yes, in general istikhara maybe for a certain purpose, but it is not beyond Allah to help His servant in any way, form or shape if He wants too. Allah gives according to our intentions. Period!