NEED it? Who said anything about NEEDING it? It's all about WANTING it....
This CBA and LBA knows no logic - it's all to do with sentiment. I know - I am a sufferer too.
But - I solved my problem. I was a very happy K10D user, but was severely tempted by the K20D. Should I? Shouldn't I? etc.
So I told myself (and SWMBO) that I most definitely needed a second camera body, as I have so many lenses due to LBA. So I bought a K20D body. Simple - problem solved!
Now - I have TWO camera bodies, and look like a real pro. I have my Tamron 18-250 on one, and the other carries whichever lens I'm using for the session - tele, wide, macro, whatever. Walking around with two camera bodies slung over the shoulder, one with the 18-250 and the other with the Sigma 10-20 makes me look so much more professional than your average tourist...
Of course, SWMBO (She Who Must Be Obeyed) insists on "lots of nice pictures" and I have her well educated in the fact that to get these, I need - absolutely essential - LOTS of different lenses. Each one is the best for something, so I need them all, just in case.
But she still refuses to carry the big backpack with all the lenses in, the lazy woman.... I've even offered to get her one on roller wheels, but she tells me that it spoils her image and detracts from her shoes...
AHA....!!!! So, THAT is the key to the whole situation. She buys shoes (I call her Imelda) and I buy camera stuff. The arrangement works well. She has given up asking about my camera gear, and I no longer ask her how much she has spent on the two rooms full of shoes. Perfect!
Of course, we had to sell one child into slavery, and the other for organ donations, to support our habits, but that's just the natural cost of living with CBA, LBA and SBA (Shoe Buying Addiction).
So there you have it. Buy the K20D - you only live once. Get it as a second camera body, and keep the K10D. Become a REAL pro and learn to walk around with both slung nonchalently over the shoulder. It builds up your trapezius muscles quite nicely too, which keeps you looking young and fit for HER.
The sacrifices we make.....!