There are advantages to the old bikes. Simplicity, a big flat comfortable seat that you can actually move around on, sit on the front, sit on the back for a while, put one foot on the rear peg for a while, then the other, then both as you slide all the way to the back... Very comfortable riding position. Once you get all the maintenance caught up they are as reliable as anything new. Brakes and suspensions can be easily upgraded.
Not as powerful as a big inline four today, won't corner quite as well as a modern sport bike, but do you really need all that on a road trip?