I think Carrara 6Pro is an extremely good tool to learn (and it is not that hard to learn at all) and worth the time. It has a greater scope than Poser, and you can actually import Poser files and manipulate them. It takes a tiny bit of getting used to, but then you could in theory do without either Poser or D|S.
I think the latter has some advantages over Carrara in posing (speed is a consideration), and it's free, so I would certainly keep it in the toolbox.

Yes. Learn C6. It broadens your horizon and you can really dive into a new realm. Do some search over here to see what Shonner has done with procedural skin shading in C6. There is still a lot of ground to cover, but it is a great area to enter!

Especially if you want to go beyond the 'play-in-the-dollhouse-render-in-Carrara' approach, you want this knowledge. It has lots of modelling opportunities and really great plugins.

In your case it only will take time. I know it can be sparse sometimes, but at least it is free!