This may sound like professional suicide, but stop learning new tech. Spend your time learning the system you're working on. If you can't rely on the people you work with to share their knowledge, well and good - go around them. If you like the place then your time would be better spent working towards better knowledge of the business practices for which your system acts as an accelerator.
There's a simple reason why most businesses use the term "Programmer/Analyst" - every new project requires a learning curve that is entirely based in business analysis. If you are not going to work at the Googles of the world, if you're going to stay in business software, then there is always going to be a problem of hidden knowledge about business processes. The sooner you get into the habit of deep, thorough systems analysis the better off you're going to be, and, in the long run, the richer you're going to get.
Not to say that you should stagnate technically - bravo for pursuing new tech. But if you haven't spent several times as many hours learning the system you're working on as you have spent learning .NET then you haven't really done what is required to succeed at your job. Tech is fundamentally easy compared to analysis. Once you've learned two or three languages - let's say C++, VB/VB.NET/C#/Java, and SQL as a basic working set - you should be able to pick up any new language or tool quickly enough to remain professionally productive.
Learning a new system, on the other hand, is going to remain a deep problem throughout your professional career, particularly if you change sectors. If you stay within one sector you become fragile but exponentially more valuable if and only if you spend your time learning the practices which underlie the systems you work on.