One parameter that the Prophet '08 has and I very much missed on the Prophet 12 is the Envelope Delay. Now perhaps one of you P12 geniuses will tell me that, if you modulate this by that and that by this, you can create an envelope delay effect. I admittedly didn't have the chance or interest to delve deeply into the instrument, so it may be that I missed the combination of things. But the P'08 has the Envelope Delay parameters sitting right there, so that it's easy to make frequent use of them. I much prefer that sort of directness.
One thing that surprised me about the P12 was the shortness of it's envelope times. They seem to be approximately as short as those of the P'08, and far shorter than those of the Poly Evolver. This meant that there were some basic sounds and effects I had programmed on my PEK that I couldn't achieve on the P12. That's not a problem for me, since I intend to have both instruments, and in trying to imitate those effects, I actually discovered some other superb P12 capabilities - namely, the Lag. I've never before owned a synthesizer with the feature. When I discovered it, the claim others have made - that the Prophet 12 is the equivalent of a modular - struck me as being accurate.
I like very long envelope times. For some patches, such as large-scale brass, they're absolutely necessary. On the Prophet '08, the brevity of the Attack time can be somewhat compensated for with a judicious use of the Delay. Another of my favorite uses of it was to design complex patches having two entirely different Layers, and to delay the entrance of Layer B. This was especially useful with pads, so that the Layer B would enter only when a note or chord from Layer A was held for a certain amount of time. This means that some times the B will have the chance to enter, and other times it won't - which can be a very desirable effect. Probably the P12 has the ability to delay a Layer, and I just didn't discover the method. When I finally buy one, I'll be looking to create that effect. But on the P'08, it's a simple parameter ready to go in an instant. That's the way I prefer it to be.
In my opinion, considering the Prophet 12, Prophet '08/Rev2, and eight-voice Poly Evolver Keyboard, one instrument cannot replace another. They're too unique; they each have their own distinctive voice and compliment each other wonderfully. Having all three would not result in sonic redundancy, unless one is an incompetent sound designer. The PEK has an array of digital wave shapes far beyond that of the P12; even its digital aliasing can be beautiful at times. The P'08 has an endearing bright brassy character that turns shrill on the other two. And the P12 has a sophistication that leaves the others miles behind; it's nearly true that, if you can imagine a sound - any sound - you can create it on the P12. This shouldn't be a matter of contention between synthesists; it should be a happy circumstance for which we're thankful.
[Update: There is, indeed an Envelope Delay on the P12, but it's not a dedicated knob, but a soft button.]