Geof,
For simple parts the payoff isn't there. If you remember the parts I picked your brain on a little over a year ago (pump heads) you know they are a fairly simple part. I had my cousin do a run of them for me on his Mazak Integrex. I'm currently getting all of my fixtures built for my mill to finish off my lathe blanks. It's looking like the total machine time will be very close to the same, the difference being I will have 2 spindles running. The mill/lathe programs aren't quite the same (time wise) so I will probably run at 2/3 the time as the Integrex. The subspindle live tooled lathe would be a little faster than the Integrex due to faster tool changes.
So my take on this is most 2-4 op parts can be done faster (in quantity) on dedicated machines than on combo machines. The beauty of the turn mill machines is the setup time is way less than on a mill (fixture plates) because most of them hold 40+ tools. They are nicer than a lathe because you get away from most tool interference problems (at the expense of longer tool changes). I feel once you get into 5+ ops or a true turn/5axis part, a combo machine will come out on top.
Now the cost factor also comes in. I'm going from memory on the pricing here so don't flame me too badly. A live tooled subspindle lathe with y axis from Mori (8 and 6" chuck) was about 230 000usd, and the Doosan was about 160 000. The Hyundai was in between and DMG was up there with Mori. To get a tooled up mill turn machine you are looking at 400 000+. These prices are from about a year ago, and I bet they have dropped off a bit.
The things I don't like about the live tooled lathes are: tool interference, limited tool pockets, (which becomes a bigger problem with live tools and a sub), very limited y axis (most machines only have 3-4"), and limited power on the live tools. The mill turn machines get away from most of these short comings, but unless you are doing high dollar aerospace, or medical work (or some other high dollar niche) you are working to pay for the machine, and not making anything for yourself.
Now you could go out and buy 2 Haas SL-20s and a VF-2 with a 4th for less than the Mori live tooled subspindle lathe and have very close to 3 times the production, with more capabilities. For a little bit more than the cost of the Mori you could add a robot to the mix and really go to town.
I hope you can make some sense out of this long winded post.
On all equipment there are 2 levers...
Lever "A", and Lever F'in "B"