Great idea, find some non-Christians who are prepared to come to your church as 'mystery worshippers' to provide an objective view on what you do. It's being trialled in the Midlands, using people who normally inspect shops.
Here's the CRE site, who are organising it, with the help of Ship of Fools who have been doing this for years, but on a more ad hoc basis. (good review of our local Wells Cathedral here). Actually organising it and using it as a way of helping churches to reflect on what they do is a good idea.
So, is your church brave enough to hear the truth......................?