All in the spirit of constructive discussion. I can think of three other (possible retail) uses for C/R's, just to throw more gasoline onto this funeral pyre: 1) to isolate the speculation that a change in dividends is imminent. A rise in dividends will depress the calls and inflate the puts, so a conversion will rise in value if there's an announcement that dividends are going up -- conversely for the reversal. 2) to isolate the speculation that interest rates are changing (a horribly inefficient way to do this given the gamut of interest rate futures that are available). With interest rates near zero, reversals will rise in value if interest rates go up -- this is the so called rho risk. 3) A conversion can be used like a "bullet" to skirt the uptick rule. If you have conversions in your inventory, you can sell the long underlying, on a downtick if desired, to expose the synthetic short.
Before I cry uncle and doff my toupee to you for your persistence (and insight), I'm going to nitpick a bit #'s 1 and 2 are a bit of a stretch for the retail guy for practical usage... but I can't argue the merit of the idea. As for #3, why would you need the conversion in your inventory to skirt the uptick rule? Why not just put on the synthetic from the get go in order to get short?
My example was a sufficient condition for shorting synthetically without an uptick, not a necessary one. Depending on your trading style, you may find it easier to sell long stock off a conversion (or a bullet) in order to go short, rather than placing option orders, especially with the premise that the market is declining quickly with no uptick in sight.
Do you want to stay long the stock and be perfectly hedged for a while? Then you can unwind the c/r before exp and stay long the stock.