Is it a good idea?
Yes and no. StackExchange is application-neutral, so unlike support in your own forum, people may and will recommend to use another app instead of yours even if the question title contained your application specifically. Therefore, questions that refers to a specific application may be generalized so it may be answerable with other applications.
Are there metrics about when it makes sense to redirect user questions to Android Enthusiasts?
Although the "too localized" criteria is sometimes applied quite inconsistently, it still applies that if a question is written in a way such that only the Original Poster can benefit from the question, then it is going to be closed. Questions in StackExchange have to satisfy the criteria of applicability to a more general audience.
Also, we generally frown against questions that requires specific expertise in a specific application because we do not have the necessary expertise to answer the application. Redirecting user supports to this site would only work if you also redirect application-specific experts to this site.
Finally, the QA format of StackExchange is not suitable for extended discussion. If a troubleshooting requires extended back and forth discussion, then this is not the right place to do so. If a question needs extended discussion, you are certainly welcome to do it on Google Groups and then write a self-answered question that summarizes the discussion (after tidying up the unrelated discussions).
If these seems acceptable to you, I don't see any reason why you should not redirect users here for support questions.