When gas prices were at $4 i think a second vehicle penciled out. At current gas prices and for the foreseeable future i'm not sure they are worth it unless you maybe have a 3/4 truck to pull your camper and supplement that with a small car that gets excellent gas mileage for around town.
I had a motorcycle for the last 10 years that i rode to work for about 5 months out of the year. Got 40 mpg vs 10 in my truck around town. Bought it for $6,800 sold for $3,000. The money I saved on gas and maintenance on my truck in those 10 years pretty much paid for maintenance, insurance, depreciation on that bike. At most the bike probably cost me $1,000 for 10 years of riding.