Hi, Cory.
The specs on the 2012 Roam 1 look more or less similar to a mix of today's Roam 2 and 3. It has mechanical disc brakes, like today's Roam 3, and a 3x9 drivetrain, like today's Roam 2. All current Roams, including the 2015 Roam 3 you're considering, have hydraulic lockout forks, whereas the 2012 model has a mechanical lockout fork. I'm not savvy enough to know the practical difference between the two, but I presume the hydraulic actuation is an improvement over the mechanical type. The 2015 Roam 3 has rim brakes, which work fine, but these have been phased out on all Roam models; all current Roams come with disc brakes of some kind -- mechanical on Roam 3 and hydraulic on Roam 2 and above.
Of more importance than any of that, though, is personal fit and the condition of the bikes (in that order). What frame size will fit you best, and what frame sizes are these two used options? If both bikes fit you the same, and both are in similar condition, then I'd probably favor the 2012 Roam 1 just due to the higher grade components. There's value, at least to me, in a bike that truly has been ridden "only a few times".