SharePoint has transformed my career in a such a positive way, I have become a huge advocate/evangelist and have a lot of passion for this technology.
I will say my career/role shift from technical business analyst into systems integration and application development can be almost directly attributed to learning SharePoint.
Quick background - Had previous IT infrastructure experience before I went back to university to get my bachelor's degree. Studied business and MIS, eventually was recruited to work for a company to basically do financial analyst stuff. The company implemented SharePoint version 2.0 soon after I got there. Having some minor exposure to the product previous to my employment, I was put on the project team for the initial roll out. I implemented the first SharePoint portal for that company (and it was a crappy one let me tell you) and I was hooked even with all the failings of SharePoint v2!
Fast forward a few years, now I'm a full time developer, integrating legacy business processes and applications into the SharePoint environment. FAR more interesting than writing pro forma budgets or forecasting maintenance costs...
So I will say this - SharePoint is completely worthwhile to learn.
On Training: There are a ton of training materials available for WSS/MOSS, from end user all the way to architect level.
For an experienced devloper I think the most valuable training you can attend is an administrator's boot camp. Getting such a deep dive into the guts of SharePoint is super valuable, from these aspects:
- Server side debugging and troubleshooting efforts on SharePoint apps.
- From a solutions engineering perspective: Understanding what can and can't be done in SharePoint and most importantly - why
- Having a deep understanding of the OOTB features of SharePoint so you can leverage that functionality instead of recreating the wheel constantly
I hope this helps answer some questions. Good luck!