I cache with my kids as well as just with my husband or parents. I agree that there is a lot of trash in caches and if anything, we will leave more than what we take. With three kids, they often each want to trade something, so I've gotten them to choose a "theme" - my son collects key chains and my daughter collects buttons/pins - things that are plentiful in most caches - my four year old will take the trash and is happy with it!
I do like finding nicer things when I'm out caching with my husband or parents though. The only problem I have with this is it gets expensive. My mom and I found 12 caches in one day while I was on a business trip recently and if we were trading items costing even $3-5, that would add up fast. Being from Wyoming, I have seen some caches along the interstate to trade book's/dvd's/cd' etc. - so there are some out there.
I think having a cache with nicer things would start out good, but even if there are only adults trading, I think you'd end up with cheap items fairly quickly as most people (including adults) don't trade quality items to begin with and don't trade equally (they think of it as one-item-for-one-item not value-for-value). I also don't think that the guidelines were put in place to "protect kids" as much as to protect all of us from stupid people! I recently found a cache in a fairly well visited scenic view spot that was in a large glass jar and there was a live rifle bullet in it. Of course all I could think of was someone dropping the jar and a piece of glass firing off the bullet and killing someone (like me (both the dropping and dieing - since I can be a little clumsy!). Not always a lot of "common sense" out there! Or as I like to say, un-common sense because if it was so common, more people would have it!
Not a terrible idea though - I guess the question is - are you caching for swag of for the "journey"? OK, didn't mean to sound to idealistic there - I like getting the "cool" swag too!!!
The "R" of Team RoKKK'M