I live in NW WA too (Olympia). I've had my Stearman here for only a few weeks now so my opinion may be jaded. I've been flying my Cub here for 6 years though.
It really comes down to whether you really want an open-cockpit biplane or just like the romantic thought of it. I'll rotuinely fly it with not much thought down to about 45-50 degreees, but the flights aren't much fun beyond 30-45 minutes, and become a real test of will if you're doing any XC flying in those kind of temperatures. However, if you only get a handful of em; the sunny, clear days when you can see all of the mountains from one point and fly in a T-shirt and leather helmet make the rest of the year worth it!
As for cost, insurance will probably be cheaper depending on the hull value and how much T/W time you have. if the N3N has the original Wright engine you'll burn 13-14 gph and about 2 qts of oil every 9-10 hours. That's a pretty good fuel burn for a radial, and probably in line with the big bore opposed engines. I used to have an O-520 in a T-34 and it averaged 16-18 gph. If it's got the Lycoming 300 or R-985 you're looking at 18 and 25 gph respectively. The difference being that the O-520 moved me at 150kts, my radial propels me at 93 mph.
The cost to get a Continental, Wright or Lycoming radial overhauled is about the same as any 6-cylinder opposed engine. Maybe even a bargain considering you're looking at least 7 cylinders. You're looking at about an outright cost of about 20K. There's several good well-known overhaulers just like for opposed engines. I don't know what a 210 or Maule goes for these days, but the nicest N3N in recent years is probably around 90K +/- and only goes down from there depending on the recency of restoration, time on the engine, and how often it flies. A newer restored Stearman goes for 130K or so. The N3Ns are neat planes, but there's no parts support for them. Stearmans have a couple of purpose-built companies dedicated to supplying every part you could need. They're not cheap, but cheaper than genuine Cessna or Beechcraft parts. http://www.dustersandaprayers.com
, and http://www.airrepair.com
Finding a good, local mechanic that knows antique airplanes and radial engines may be your biggest challenge. Fortunately, there's a good suppply of them at Olympia. feel free to email or call if you end up needing some more info, a pre-buy or a checkout. If we go fly, it may unfairly sway your decision. The N3Ns is probably easier to land than a Stearman depending on what wheels it has. In the air both are very solid and stable and can handle a lot more cross wind than you think. They have great rudder authority and are heavy enough to not be kit-like (2,000+lbs) Do not believe the horror stories you read about Stearmans/heavy biplanes, etc. Yes, there's no visibility over the nose, but there's none in the back of a Cub either. Keep it straight and it lands just like any other taildragger.
That said, the N3N is a rare classic, a combination of throw back 1920s styling, with some government mandated truck-like construction. Actually, except for the orignal thin pie-pan wheels it's probably better than a Stearman. All metal fuselage, solid tail struts, and ailerons on all 4 wings. Designed and constructed by a firm that wasn't concerned with costs or profit, overbuilt and solid; Naval Aircraft Factory
As a 70+ year old bi-plane, you're probably not going to want to be criss-crossing the Cascades or bagging strips with it, but that's not what it was designed for. An early morning or sunset flight followed by a smooth roll and loop will put a smile on your face though.
Bottom line, if your wife wants to travel fast, and in comfort, an open cockpit of any sort probably isn't your answer. If you guys like short trips for lunch, and nostalgia, or the old girl (plane not the wife) being treated like royalty at fly-ins then the N3N is your magic carpet!
Lastly, who knows how much longer radial engines will be around, my prediction is we may be the last generation to see them operate as the expertise and parts to overhaul and maintain them is slowly disapperaing. I for one, am sworn to fly mine on a regular basis so my young sons will always remember the sight and sound of an open-cockpit biplane, as their kids surely won't have that priviledge.