A couple other tactics.
When possible, a trade is better than a cash buy. Most of us have something someone else wants, and if shipping is the only $ involved, it rarely is an issue.
Too many hobbies can be a problem. I used to have drums, bicycles, mallet instruments (try explaining why you need tympani in the house!) and grills. I'm down to bikes and grills now, and just parted out a bike for a profit. Hard to argue about kettles when you deposit money in the bank.
My wife loves yard sales, and she loves a bargain as much as anyone. She's not quite as tuned into looking for kettles yet, but she's getting there. I need to make her a cheat sheet she can have in the car - kind of an illustrated "what to look for" reference. I'll come up with something in the next week or so and maybe we can all use it. Nothing better that making them feel a part of the fun!
For every grill you keep, give one away to a family member - especially if it's her family. (well, maybe not one to one..) I've given 8 or 10 away by now, and she LOVES seeing my SIL getting into doing all the cooking.
Spend time in the kitchen too. Don't limit your cooking to the grill. It goes a long way to become adept at all types of cooking, and the fact that you choose to fire up the kettle is just part of the routine. My wife prefers a gas grill, so I keep one in good shape so she can use it any time she wants.
Host a family + friends party in the Summer so you can demonstrate why one grill is not enough. We do the 4th of July every year, and I have several grills up and running all day.