The biggest problem with these twin v. single debates is that they usually fail to separate the two very different things
1 - stuff which only a twin gives you
A spare engine
At the top piston end (e.g. a C421) loads of payload
and speed
2 - stuff which a single can give you but is more common on twins
Full de-icing
Redundant electrical systems (see Cessna 400 for an example)
Good capability versus weather
Pressurisation
One would be a fool to be flying a twin to get a high operating ceiling for example, when any half decent SE IFR tourer can go to 20k and the turbo ones can do 25k.
If I recall right, the NTSB data shows SE turbines about 5x less likely to go down than piston twins. Now, this could be hiding a lot of factors, for example the population of SE turbines is likely to be younger and better maintained than the population of piston twins (just look around your airfield for ample evidence of this).
The extra cost of a piston twin is high. I reckon the total operating cost of a Meridian and even more so a Jetprop is going to be similar to the OC of a Seneca or something similar. Well, after the capital cost has been set aside
