Would a competent asp .net C# developer be disregarding a lot of their skills in order to have more concern with configuration and server-side coding when moving their career into the sharepoint 2010 arena? Or is asp .net C# in fact just a good base to begin the study of sharepoint on?
ASP.NET and C# are excellent starts to being a SharePoint developer. SP web parts are very similar to ASP.NET controls. In fact, I would hire anyone with ASP.NET and C# experience and no SP experience to learn and develop in SP. I think being a solid .NET developer goes a long way in the SP world rather than the other way around.
It's true, that ASP.NET experience is beneficial for stepping into Sharepoint development considering Sharepoint itself is developed in ASP.NET Webforms, but the underlying ideas of the two are very different. ASP.NET is a framework where as Sharepoint is a full blown development platform.
While you code everything yourself (in a figure of speech) in ASP.NET you won't be developing for Sharepoint like that. Most of the time is spent configuring and molding vanilla Sharepoint into something that is of value to the client.
Sharepoint does a lot for you and that's great. It's ease of page editing without any app redeploys and coding skills holds great appeal for the clients, but it's still very rough around the edges. No change is as easy as it should be and you will be spending a lot of time fighting with the obscure API of SP. I don't remember the names of the API methods that turned a few of my hairs gray, but i swear there were a plentiful that just wouldn't work and the other lot that had no documentation.
There are many quirks and do-not-touch areas, that all beginner Sharepoint developers sink a lot of time into on their first try with the platform. Considering the amount of XML you are forced to configure i'd say a step into Sharepoint gives you a good insight of what Java EE developers go through. My point is, ASP.NET experience is helpful, but it doesn't get you very far. Sharepoint is HUGE and a speciality in itself. IMO not something you would easily "master" under 3 - 5 years of experience.