Most definitely keep the Sigma 17-70. For general everyday stuff and travel, this is my most often used lens.
Since you mentioned shooting wildlife, the Bigma is a natural choice, but it wouldn't hurt to pick up a lightweight tele like the DA50-200 or DA53-300 for chasing the kids around with or for traveling.
After going on vacation, I've come to a renewed appreciation for my zooms.
Since neither are that heavy, they're not hard to carry around in a smaller bag.
When choosing lenses for my kit, the most important thing for me is usefulness. I ask myself what a particular lens would lend to my kit and make my decision based on the answer to that question. There's also financial considerations to consider, as well, as I really can't afford to have expensive (but wonderful) lenses sitting around that I'm not using.
Finally, the less lenses you have, the less lenses you have to keep up with.
Simple is good.
Heather