Everyone sees things differently, but here's my perspective.
LTE will have little effect on app development outside of media streaming. Even media streaming apps will still be usable on the X, either using slower EVDO or WIFI at the same or faster speed than LTE.
The Droid X is at a unique period in Android development. It's going to perform very well running apps that are designed for the most common platform (droid1 or snapdragon 1Ghz based phones). So using this software will deliver a premium experience on the device. I'm guessing the next wave of devices, such as the 2Ghz phones that are floating around out there, may launch with Gingerbread and run newer, more cutting edge software. However, as a first run next gen device, it'll be slow in running those new apps. Then this time next year, new phones will run that next gen software even better.
Irregardless, the DroidX will be a good phone, if not great. I'm excited to see what the future holds for it.