Let me add a bit to what Larry has said.
Range: Most 337s have long-range tanks with about 125 gal of fuel. A non-turbo model burns about 20 gal per hour with a ground speed of about 150 knots, so you can safely go about 5 hours or 750 nm.
Maintenance Costs: Comparable to other twins (which is still substantially greater than for a single-engine, fixed-gear aircraft). Key is to find a mechanic familiar with 337s.
Easy to Control: Arguably the easiest to control of all twins.
Summary: It seems to me it all boils down to one question: do you think you need a twin? If the terrain you fly over (mine is mostly over water) or your concerns about engine failure or other factors warrant having a twin, then I think a 337 is a superb choice. Most bang for the buck (337s are generally less expensive than other twins) and an easy-to-handle aircraft.
More Reading: An entire web page for prospective buyers of Skymasters exists at
www.skymaster.org.uk/purchase.asp and covers most of what you have asked and more.
Ernie