The GI who placed Emily's tube/Mic-Key told us that he saw better results when the button was NOT replaced every 6 months, but instead, changed when it needed to be changed. Over the years he saw more granulation, staph infections around sites and poorer healing sites (after removal) when the button was "monkeyed" with (his words) on a regular basis. He said to change it when it needed it. I had huge reservations about this. Just didn't seem righ to me, but we went with it, and it's been fine.
We know we need to change it when the site starts to "leak" or the button starts to sit funny on her tummy. That's what we follow. I'd say it works out to about every 6-7 months, anyway, but we just watch carefully for those signs.
As far as care, we wash around the button with warm water when Emily gets dressed in the morning and when she puts her jammies on. And, of course, it gets a good soaking in the tub on bath nights. We do keep split IV pads around/under the button. This keeps her skin from getting irritated and keeps the site dry. Before we did this, granulation was a big problem. At any sign of redness or irritation now, we apply triamcinolone under the iv sponge.