When you "root" all your doing is gaining "super user" permissions which allows you to modify system structures you wouldn't normally have access to such has the ability to over clock the processor. So yes you can root, and keep the same ROM. If you know what your doing , there is no reason to wait for the one click root, but if you are simi new i would wait. They are the same root, just the steps of the manual one are more intense.
If you manually root or one click root ( the same thing ) there are ways to un root the phone yes. Is it easy on the inspire , not sure yet.