SAR cover does not require a Nimrod, it's just that until recently we had Nimrods and they were very good at it.
Top cover to helos in the SWAPPS was quite common - the Nimrod would search the area, conn the helo onto the target so no time was lost getting to the winch operation, and provide the helo itself with a bit of extra security flying so far from land.
Yes, a helo can winch when a Nimrod cannot - which makes a difference on those occasions where the survivors can all fit into the helo. (Might have been difficult today).
No, people don't decide they prefer the colour of a Nimrod dropped dinghy, sometimes dinghies are damaged, sometimes they cannot be successfully launched, sometimes - in simple terms - whatever survival aids are provided by the ship prove insufficient..... a foolish point you made there.
No, the average SAR chopper won't reach 30W (check the map) - and when incidents occur far from land Nimrods would do a surface plot and vector the nearest shipping to the casualty. They did this a LOT of times, people were rescued by ships that were often (usually, in my experience) unaware of the need to divert to help prior to being called by the Nimrod. Our area of responsibility extends to 30W - today the MPA job in OUR area was performed by a French aircraft.
The MPA SAR role does NOT need to be performed by a Nimrod, but it does need to be performed by some fixed wing asset, which we patently do not have or it would have been used.
As for £ per life saved, thank Christ you aren't running things, it'd be cheaper to just let everyone drown, after all.
Dave