You guys make it sound like developing is bad.
Depends on your playstyle. If you're RPing or playing tall, developing is fine. Even in these scenarios, however, taking clay is often more worthwhile to gain more develooment. Base full core cost is 10 ADM per dev (vs. 50 for developing) plus some time, manpower, and ducats, which are much more abundant than MP.
If your're trying for WC or min/maxing or playing MP aggressively, it's not worth it to develop. As you point out, DIP and MIL can be in abundance, especially in the early game or if you have a 6/6/6 god-king. Then, of course, it's better to develop instead of just wasting MP, of course, but those points are usually better put to use coring, annexing, ideas, and blowing up walls (in the later game).
In any case, I think we've shown in this thread that moving your capital probably isn't worth it for development no matter your playstyle, assuming it's of a significant development level already.