I concede both your points, though I still think an older actor with less makeup needed would be preferable.
Also, if Picard is supposed to be in his early 70s, think about how even he'll look in 30 years. A fair bit older and more weathered than the gentleman on the cover of Mission Gamma: Twilight
, I'd think. But then again, this is Star Trek, where there's a tacit assumption that what we as the audience see isn't exactly what the characters themselves see.
Boxleitner's voice is an interesting option for Vaughn's, though. I'll have to reread some of his scenes and try to hear it.