I'm fully involved in my local church

That sounds a good reason for ignoring mission - but someone might suggest that you could be so much more useful there if you knew about a wider field.... like, for example Crosslinks work!

You need to make it sound as if you have received an email from heaven telling you that involvement with your local church gets you time off for good behaviour when it comes to missions. But do even you believe that?

You're on good ground when you can honestly say that you are well-involved locally... the weak point in this argument is that a broader view will help you and the local church. And have you ever considered that God might have been training you in your local church so you can serve him somewhere else?