Rob, what you have described concerning Bell, (ie. his reliance on secular scholarship), is one of the roots of Liberal theology. Don't get me wrong I don't know nearly enough about Rob Bell's theology to call him liberal, all I am saying is that Liberal theology came about in part because the Christian thinkers of the 19th century found their theological and philosophical roots in the prevailing secular culture of the day. They placed secular thinking ie. modernism and secular science ie. evolutionary theory before the Scriptures and consequently headed down the Liberal road.

We have to be very careful how we attempt to understand God, if our starting point is anything but the Scriptures we will end up in trouble. In a culture that is driven by technological change and scientific advancement it would be easy for us to think that because something is new it is therefore better. Historical theology, (ie. surveying what various people have thought about God through history), is important but not to the detriment of Biblical theology. It is far too easy to get caught up in various people's ideas about God and what the latest thinkers are saying, both secular and theological, but at the end of the day our primary goal is to know God, (full relational knowledge not just head knowledge), so we can make Him known, and our God has revealed Himself through Scripture.