IIS7 web farm - local or shared content?
Solution 1:
Your concerns are valid and at the end of the day you will either have to assess each reward with its inherit risks.
Shared Content is great; but as you pointed out you then have a dependency on a remote host, and clustering storage technologies isn't cheap or simple. This type of setup has its place, and given your current solution I assume you aren't looking for a 99.999% uptime solution.
Have you thought about extending your script to disable load balanced nodes (at the firewall) during times when you sync content from Web1 > Web2?
Shared Config is great though, and uses a local cache copy if your UNC share is unavailable, and is a great way of ensuring web apps have the correct configuration.
My 2c's
Solution 2:
Shared disk on a SAN is the best solution - however only a little more realistic than flying on a broom. Some vendors like Melio offer it - but some big downsides (expensive, need a SAN, if on VMware lose ability to snapshot w/ shared controller)
Solution 3:
We have been using UNC shares to serve clustered (NLB) webheads for some time and recently moved to 64 bit OS Win 2008R2, the difference is huge, no more concerns about exhausting SMB connections. There are limits but they are high. I've just added DFS into the mix with another file server but I can't speak to reliability yet.