Is Re-gearing worth it?

No doubt gears will help the wimpy 4.6. Mine is a '97 which is even more gutless than yours. I don't think I'd jump all the way to 4.56 though. In fact I went from 3.55 to 4.10, which REALLY made a difference pulling my trailer. It also improved city driving immensely! After regearing it was much more fun, AND I got better mileage. Highway driving was more enjoyable, the engine almost never dropped out of Overdrive anymore. Before, it would drop down at the slightest incline. I lost a couple mpg though. Towing was MUCH better. Living where I do, mountain towing is a given and my trailer is around 5500 - 6000 lbs loaded. The 3.55 geared truck almost stalled out a couple times climbing hills, down to 20mph and still falling by the time we crested the hill/peak. The 4.10 geared truck NEVER experienced that. Not that it was a tow monster, but it was certainly competent. I think 4.56 gears would be overkill and could render your drive train quite a bit weaker.

And on a side note, even though the RPMs are higher, I get better towing MPG with OD locked out.