The reason for the tire machines is because it's a money maker/saver, especially when compared to any other tool that may be purchased. Even if you only use these machines for your own cars (yours, wife's, kid's cars, MIL, FIL, bro, sis), you're saving a lot of money. Next time you buy tires, look at the itemized breakdown and you'll see that you're paying for dismount/mount, wheel balancing, shop fees, EPA, etc.. You're easily paying $100-150 for Installation, on top of the price of tires (which have also been marked up 20-50%). Also, most people buy tires every 2-3 years, some even more often, depending on their commutes, suspension/alignment issues or lack of other PM. You also don't always get 40k miles out of tires rated for 40K. Some folks also like switching to winter tires on they're same rims, which cost money each time you do that. I know these are not machines for everyone but the OP definitely has the space for them and if he's your typical GJ type, I'm sure he's doing his own maintenance too.
Finally, everyone who's raising kids knows that it cost a fortune nowadays, especially if they're playing sports, are into dance, music or any other type of extracurricular activity. The OP is covering all of this and will of course continue to do so after the deadbeat dad "completes' his obligation. If the guy has a hard time keeping up with payments now (which are federally mandated), do you really think he's going to be kicking in anything after the court states that he's officially done with child support? Hell no! Do you think the OP is going to stop being financially there for these kids, especially when at 18 they're still living at home (like a lot of kids do nowadays)? No, he won't. In fact he'll continue to take it all on because those are his kids and he's going to keep doing the right thing. Letting him "have" $1000 back, from the tens of thousands he's already spent on them, when he wasn't even legally obliged to do so, is perfectly fine. The mere fact that his wife gave him the go ahead, shows the level of love and trust that she has in him. Also the fact that he's trying to carefully plan for the use of this money should tell you something too.