If I were in your shoes I'd buy the 5D3 in a heartbeat! Obviously you have the money, you do not need to justify it to anyone--unless maybe your spouse. You do not need to be a pro, you do not need to make money from photog, you just need a passion for photog like most of us CRers. Do you need a 5D3 or FF body for that matter? Probably not, but so what.
I have a 7D and a few nice lens, I'm happy with all my gear. I do not have funds for a FF body yet, but I plan on adding (not replacing or "upgrading"), to one when I can. The hard part will be justifying it to my wife, 3 plus grand is a lot of money to me. What the hell, its my hobby, my passion, my escape in life.
I suggest skipping the 5D2 and go straight to 5D3 if your heart is set on it otherwise you will always wish you did. Yes, a 5D2 will save you some bucks for another lens, but who says that you can't get that lens a little later?
Even though I'm not in in the market for a FF, what I'm reading about the 5D3 sounds like an awesome piece of technology. And I do understand some of the disappointments that many have posted.
Get your 5D3 and enjoy!
Edit: Don't get to hung up on all the negative comments on the 5D3. It seems most of the neg comments are due to disappointments in expectations and not defects or some other product problem. Like I mentioned, I honestly understand and in some cases agree with many of the comments and disappointments.