One other consideration -- VTL will insist you use their tubes. A full set for a MB-450 II or III will cost you north of $1600. Using any one else's tubes you will run into maintenance issues with them (I'm not saying they won't work, just that VTL are fussy in this regard). Of course the II and III have full protection and auto-bias so they are a cinch to use but important you have the heads up on cost of ownership
Finally on the Gen I -- I'm sure it's still a fine amp, but not reflecting the current VTL design philosophy and outside of a trusted dealer relationship not sure about how easy to maintain it will be (although the design is such that I'm sure any competent tech can do it, I've done routine repairs on my amps myself (replacing binding posts I managed to snap off) so they are easy to work with)