If we use a whitelist, I'd probably remove the GriefPrevention plugin (land claims), because they create annoyances with minecarts, liquids, pistons, etc.
Mojang has announced 1.6 is going to be released sometime this week or next week. We don't have to start a new world, but horses will be difficult to find in existing biomes. I think 1.7 (or whatever comes after 1.6) will be a better time to start fresh with a clean slate because it's speculated there will be large changes to world generation, primarily new biomes.