@Eug, my wife and I are in our early 20's and in college. We don't have plans to keep making 15k per year, but for the time being we're trading off working part time, depending on who has the heavier semester. I'm close to graduating with a bachelor's in geology, and I plan to work while she pursues higher education in the humanities (even if it doesn't have a fantastic return, because it's what she wants to do).
Yeah, that's fine. Living as a student or even a post-grad on $15000 is fine... but those are the early years. You have to start somewhere. But the key is you're aiming higher, and I suspect this higher target would become even more acute if you had a kid on the way.
As for owning that boat or plane or whatever, not really. Around here it's owning a cottage, but they're all potentially money pits (even the boat, because of docking fees, etc.).
The other problem with all of those is the time requirement. Unless you're making a big wad of cash, you're probably going to feel the need to spend time every year at that cottage, much of it thawing it out for spring and closing it down for fall, that is if you live in an area where cottage country is dead for the winter. I'd rather just save my money for retirement, and rent that cottage every few years. Even if I had to spend $8000 to rent a high end cottage for 2 weeks, that's heluvalot simpler than buying one for $600000 and wasting my time managing it every season. And yeah, maybe next year I don't want to be at the cottage, and would rather visit Europe or something.
P.S. While it's common for people to have part time maids, it's very uncommon these days for people to have butlers. That is a dying profession, at least in Europe, and it's virtually non-existent in North America. The ironic part is that if you're a big-wig butler, you can make 6 figures.
P.P.S. I ran into Kevin Bacon on a commercial flight a few years back. No, he doesn't have a plane. Apparently he has a net worth of about $50 million. Is he not rich?