What would you want to see in a vocabulary program for late elementary students?

I'm trying to figure out what I want, and deciding I may need to create it myself.

I want a program that isn't full of $50 words. My oldest son is learning lots of $50 words in his Latin studies -- quintessential is his current favorite -- and will be learning lots more as we get further in Greek. 

I want words that you can use in conversation with anybody, wherever. The checkout lady at the grocery store, his scout leader, the barber, anybody... where he can finish the sentence without the other person raising an eyebrow at his 'fancy-schmancy' vocabulary.

I don't want a simple "word a day" thing where you spend two minutes learning about a word, and then assume that they now "own" the word. I would like something a bit more spiral -- so a word, like confide, is used in part of the description of another word on one day. A few days later, we'd actually study confide, learning what it means -- but if it is a word they didn't know, they at least would have heard it in context recently. We use it a bit. And then over the next week or two, we use it in other word study a few times.

I don't want to be filling out a bunch of worksheets, or doing word-search puzzles, or other busywork-looking activities. I wouldn't object to some type of computer reinforcement - matching games, for instance. Or to some crossword puzzles now and then. Mostly, I want to be learning about the word, and then actually using it.

I want something that could be used with multiple ages, with some adaptation. So my 4 year old can listen and make up his own sentences. My 2nd grader, similarly, could mostly do things orally, maybe doing doing copywork of some worthwhile (and short) saying. My 4th grader could do the above, plus create his own simple dictionary. My 6th grader could be required to go to a dictionary or thesaurus and find more etymological information, or spend some time differentiating between some synonyms. 

This is all totally off the top of my head! I have no idea what would be age-appropriate for some of this. I just know that I want to start doing something and have it work for all of them.