Oh its absolutely worth learning, shoot COBOL was worth learning just for all the money I made fixing the 2K bug, and its really a dead language. I think multiple languages is always good, I just think that you are likely to use your C++ more, and wouldnt neglect it because of a fascination with ADA. Plus there is alot of Legacy ADA stuff out there. Maintence of current legacy systems is over 1/2 of what we end up doing, so being able to help with a program done in ADA, Jovial, Forth, C, C++, always makes you a better candidate for a job.
-Tig