An airbag is available on the 2006 Gold Wing:
http://powersports.honda.com/motorcycles/touring_sport_touring/model.asp?ModelName=Gold+Wing+Airbag&ModelYear=2007&ModelId=GL18B7
Re the OP's question, the answer is definitely an Airhead BMW twin, the air-cooled models ending in 1995. Not fast, but reliable, relatively smooth, and rebuildable forever (not that they'll need it). There's a solid body of knowledge at the user level (start with the Airhead Beemers Club,
www.airheads.org). Not much goes wrong, and everyone knows how to fix/prevent the things that do - they're simple bikes. Parts aren't particularly expensive, and they're readily available (to start, go to
www.bobsbmw.com and request or download a catalog). The bikes are also easy to find around the country (
www.ibmwr.org/market). Airheads are more refined than any Sportster made before 2004, and vastly more livable on any kind of a trip. They're the 123/126 diesels of motorcycling, and they'll be around forever.