The dual M1000 will cost you more in the end.
They are 30+ years old, both will likely need service soon-ish. Recapping and power supply replacement are almost guaranteed on those if not already done.
Midi control sucks. Upgrading to Tauntek will improve it but only so much can be done.
On that point, you'll need something like an Alpes, Kiwi Editor, or Stereoping to even get close to matching the controls of the OB-6.
On value, they're not really appreciating. Every vintage piece of gear that doesn't blow has had a similar correction bump in the last couple years. Its relative value is just correcting for inflation. Its just not losing value any more.
That said, absolutely get two M1000 if you dig the sound more but I'd take off the rosey glasses and think on the downsides a bit more first.