I thought of something similar: When an installation fails for whatever reason it would be nice to be able to go back in the wizard, change some options and try again. It's very annoying when your installation fails because you forgot something and you have to start all over again.
It could save time during installation, if the Deployment Center gave an early warning of requirements not met.
Example: "You are using SQL Server 2005. You need at least SQL Server 2008 SP1 to install <something>".
At the moment, error messages during installation usually show up late in the installation process, and are very difficult to interpret.