OK fair enough. I looked at your "Baby" and it does look nice. You noted that it has a new rear bumper and assume that it was necessary.
I wouldn't be overly concerned though, structurally anyways. I went out and looked at mine and there is very minimal rust around the front lip and, like yours, isn't noticeable unless looked for.
It is 15 years old and should last another 15 - 50 years. It will still "Bump" like it's supposed to. Additionally I would be more concerned with rust on almost any other part of the truck / frame first.
Aesthetically it's all up to you and how much your willing to fork out to have it removed, striped down proper, dipped and reinstalled. Or take all of that money and invest in a nice aftermarkek bumper.
Yours appears to be completely stock; any plans?
I lean towards sarcasim at times but really, at the end of the day it's your call.