Should I replace my plugs?

[ticopowell]

Hey all,
I have been thinking lately that I should probably replace my plugs sooner rather than later. I have 67xxx miles and I want to have as few problems with them as possible. I called the local dealer and they didn't quote a total price(they said they would call back), but they said if any plugs break its an extra $55 a plug. Is this a good price for that? they also said that it will cost a lot more if they have to pull the heads to fix them... .
I also could do it myself at the on base auto hobby shop, but I am not sure if the trouble is worth it. I searched for some helpful links on here and other web sites, but I can't find any, so those would also be appreciated.
Thanks in advanced for all the help!

Oh and I have a 2005 F-150 with the 5.4, thanks again.