I think the reason why most IFR pilots are buying singles, while the piston twin market has all but died over the last 20-odd years, is that the accident statistics do not support the need for the second engine, and one does pay a helluva penalty for the second engine.
Obviously the individual pilot is free to factor in his own attitude to risk, but - as with TCAS and mid-airs - that view is not well supported by the accident data.