While I agree that there are some nostalgic aspects with the classic sculpts, and arguably I agree that posing the new sculpts can be difficult, I personally like to mix things together. Details on the new sculpts are very photogenic and there seems to be a "spark" in the features that some (only some) of the classic figures lack. I have, from a casting perspective, use of all of the figures, whether new or old, and can't find myself omitting either for a "purity" concern. Besides, look to the BATs. While the newer ones are interestingly sleek and trim, the older ones provide the multi-functionality (by way of their multiple hands) that some stories may require. There are other examples I'm sure, but that one comes to mind fastest.

Bayer