Been through this several times. Sadly, unlike some of my friends who regularly sell on their 2-3 year old gear, I tend to hang onto mine far too long (although some kites really do last a long time, e.g. my Cabrinha Nomad 5.5m. Three solutions:
1. Sell very cheaply to someone who might actually use it. Two examples are selling a whole quiver of old Best Waroo kites to someone in Cape Town very cheaply, about $50 per kite, although I have no guarantee they actually used them. And I recently sold two old Best bars to someone on here who wanted to build their own bar from old pieces. Asked $30 for them. We have a fairly regular stream of newbies in our little local kiting community, and folks have sold them 3-5 year old kites cheaply to get started.
2. Donate to a locate shop that sells an eclectic mix of materials to creative types, called the Idea store. They cut them up into pieces of fabric to sell on. That's where my three C kites went and my Best Waroo 14m and 2 Best Bularoo 16m kites are going. I was hoping to find something similar in Cape Town, but even the repair shops there have not found such an outlet for trashed and abandoned kites.
3. Re-purpose them myself, most simply as drop cloths when painting walls etc. My friends are disgusted at this one! An old Best Nemesis 9m, yet another kite that seemed great at the time, but really sucks.