For positions advertised by recruiters, the details tend to be vague. Is it a good idea to ask a recruiter for more information about a position before replying so that I can write a more targeted cover letter, or should I just write a cover letter based on the information I've got?
Never write a general cover letter. It is always good to ask for more information about the position - it shows genuine interest in the job and it helps both sides to find out if there is a match.
Asking a recruiter about the job is good since he will try to sell the job and you'll have a perfect starting point for the cover letter.