Thanks for getting back to me so quickly!
I appreciate your desire to keep the plugin lean - wish more creators had the same philosophy.
I'll try to briefly enunciate the couple of difficulties I see with the current implementation, though.
1) It doesn't cut down on my spam generation. I appreciate that the bot-generated "comments" go directly into my spam folder . . . but it still takes time to cull them regularly.
2) If a genuine user should overlook the Captcha, or enter it incorrectly, his/her comments will be marked as Spam, and might or might not be noticed when I do my culling (maybe a week or more later) . . . and the user will have no way of knowing that there was ever a problem, or given a chance to correct it.
CF7 has several feedback messages of various types and for various contingencies . . . obviously I have in mind something very simple, like, "Sorry - your comment could not be submitted due to incorrect Captcha".