I want to add something here. It seems like both of your posts have a goal of making expensive watches available to people who otherwise can't afford them. The specific amount is irrelevant, as what's "expensive" for one person will be chump-change for another. The point seems to be that you want to put more watches into more people's hands so that they can reap the benefits of value appreciation. I strongly question whether this is a worthwhile goal, and I must disagree that watches necessarily appreciate.
1. If someone can't afford a watch, then encouraging them to do so is, in my opinion, unethical. Just because they pay a little at a time, doesn't negate the fact that they can't afford it. You are asking someone to tie up their money in a watch, which is not good if they suddenly need that money for something. There is NO guarantee that the chosen watch will be worth anything more than what was paid originally, and in most cases, it will be worth less. A buyer will have to be found and again, a loss is more likely than a gain. If they put that same amount into an interest bearing account, their money would be right where they can get at it and they would likely be much better off financially than if they had taken a gamble on a watch.
2. If you can't afford it outright, and don't have the discipline to save your money in a standard bank account, but choose instead to pay for it via installments through a company, a credit card, layaway, or anything else, it's the same thing. You have to think about what else you could be spending that money on each month as you send in your installment payments. At worst, it is money that could otherwise be diverted to bills, high interest credit cards, car payment, mortgage/rent, emergency fund savings, retirement savings, kids' college funds, potential home repairs/improvements, etc. If these things are not taken care of, then the watch budget is eating into one of these.
3. Preferably, they are funding their watch by avoiding unnecessary spending like going out to eat, etc. (which is how I saved for my watch), but if they are doing this, then they aren't using a "pay-in-installments" method and aren't the subjects of your questions. Also, as I said previously, for someone in the income bracket that is your focus and would need the type of services you have suggested, once they saved up $25K - $50K or more, a watch would be an extremely foolish thing to spend that much money on. That much money should be put on paying off the house or other debt, or investing in retirement funds (do you know how few people have anywhere NEAR enough saved for retirement?), or fixing a leaky basement, or investing in something less risky. I promise you, not ONE reputable financial advisor would advise someone in this income bracket to "invest" that much money in a watch. "Expensive" watches are best bought by people with incomes where they aren't sacrificing much (if anything) and to encourage people to spend more than what they can afford, is like I said earlier, unethical.
3. That said, people buy things they can't afford and shouldn't buy, all the time. I believe that behavior surrounding credit cards and savings accounts prove that people do not like to save but they do love to spend and are willing to pay a premium to have something now rather than save and wait for it. But there is no need to create yet another way for people to spend, as there are already many, many ways to part foolish people from their money.
4. It seems that you are working on the assumption that watches are a good investment, but I have to challenge that assumption. Watches physically deteriorate over time, which limits their usefulness and value from a long-term perspective. Yes, they last a long time and there are many old watches out there, but they don't last forever and honestly, who really wants most of them? Look at all the vintage watches out there. SO MANY vintage watches, and MOST of them are not selling for that much. Maybe a few of them are being sold at a profit, but a profit to whom? To the grandson who inherited a watch, sure, it is a profit to him if he sells it, but it wasn't his money that bought the watch. If he sells it, he will likely get less for it (as compared to his monthly salary now) than his grandfather paid for it (as compared to the grandfather's monthly salary back in his day). And frankly, if Grandpa had put that money in stocks instead, it would probably have vastly outperformed his watch and netted his grandson more money.
5. As soon as someone puts money into a watch (whether by increments or all at once), they are not able to make that money work for them anymore. They are not earning interest in savings or another investment. If they're lucky, the watch will be increasing in value by the amount of inflation, but then, if they had invested in a traditional investment vehicle, so would their investments most likely. And the traditional investments are more likely to yield a profit if sold, whereas sale of a watch will more likely yield a loss. I've read the articles about watch values increasing, but again, that's IF you have the right watch and IF you can find a buyer willing to pay more than what you paid.
6. In summary, while I appreciate the idea behind what you seem to be suggesting, the value of the suggestion is not there. If ownership of an expensive watch is the goal, there are already many ways to buy things you can't afford right now (and it is questionable whether a person should be doing so in the first place, potential appreciation or no); and, if investment is the goal, there are already many ways to invest even small amounts of money. Finally, for appreciation to be realized, the watch must be sold at a higher price than it was bought for, and must be at a higher profit than would have been realized had the funds been otherwise invested. The premise that watches are a good investment is a faulty one, and most people should not be gambling with their limited means.