I must say, this has been one of the more informative positional discussions on these boards.
I often have questions about trading out preferreds that have a cost basis of say $3 - 5 when they appreciate to $15 - 20, and wonder whether to hold for the locked-in yields or take (one way to look at it) 3 - 5 years dividends up front and immediate with a sale, then buy into another preferred or some other yield-cow. Often cannot find something even close, so part of the calc is trading a 25 - 35% yield for a 12 - 15%, but at a larger asset base.
Looking at prefs from the same stable and considering a trade based on price differentials is a great discussion.
Back in March, this phenomena was rampant in the banking sector. Bank of America capital trust stock was yielding one thing while Merrill Lynch Capital Trust, Mer-D, was yielding way more. Both issues have the same liquidation rank (one step above the tarp). Same with the Countrywide issues. For some reason, some investors thought that the Merrill and the Countrywide might not "transfer."