You make some great points, and for what it's worth I still quite like CoC. The Miyazaki touch makes it unique amongst all of the Lupin material to come out over the years. It deserves a lot of credit for introducing the character to a wider audience.On the nature of the Lupin franchise, I actually get a bit fed up of hearing the argument that the Miyazaki/Takahata version is somehow less valid for not having remained true to the characterisation laid down by the original manga. While very few subsequent offerings have been even half as successful, I think there is enough material out there that borrows extensively from or blatantly tries to copy the tone and feel that film lays down that, for an entire generation of fans, that is their Lupin.
The fact that we can have the (mostly) family friendly hijinks of Part IV, and its forthcoming continuation, produced more or less concurrently with the adult strain that Sayo Yamamoto and Takeshi Koike have helmed, is surely proof that both interpretations can coexist quite happily and the franchise will not somehow collapse as a result.
On a side note I need another series by Yamamoto or some more films by Koike, they're gorgeously gritty.