This is one of the best discussions I have seen lately! I think that both sides can logically be argued, and lost of insights - thanks to all! I am somewhat torn on this one...
I strongly agree with those who say IF you do start over, make sure to think carefully about what you want in your portfolio and try not to repeat mistakes you came to regret.
I think that my view is that while I would probably only sell my entire portfolio if I decided to move to to something else, either different forms of investing or a different hobby or business, depending on your level of involvement, I might well sell a major portion of my portfolio to either narrow focus or have funds to move into new niches.
I think it you never even consider selling a big chunk, it MIGHT mean you are not looking critically enough at your portfolio, or not open to new trends and new opportunities. That being said, I think failure in this business is often associated with moving from one trend to another, and just as conventional investors who trade too often are shown statistically to do worse, same might be true in domains.