Buying an expensive watch or accessory that's easily lost, stolen, or broken is a bad investment, imo. Plus, it can make you a target for theft or a mugging, and losing your life over a $1000+ piece of jewelry is really not worth it, and taking out a loan to get something that you can lose in a day and that you literally just wear for looks is a seriously bad idea.
"If I can't buy it now, I don't deserve it in the first place." is a decent idea, but a better one is "If it's that expensive, I should just put that money in my savings and buy a regular watch." is better for most, I would say. As for saving 500 yen coins, that's not a bad idea, but it's better to put it in an account where it'll accrue interest rather than sticking physical coins in some sort of container. Plus, you won't lose that money if that container gets stolen or it gets lost, or burns up in a house fire.