Maybe it's a little bit of all of that? Maybe they feel insecure, knowing that you're doing well, so they feel the need to brag about their financial situation, and at the same time maybe they're dying to know just exactly how well off you are. Do they consider you closer friends than anyone else you know, or do you think the reason they're sharing is because of your financial "status"? I mean, maybe they would share financial stuff with you anyway, just because they know you so well and feel comfortable... or maybe they feel like you're the only one you know who's on the same page.
I have a handful of acquaintances who do this with political stuff. They make their views known, and they seem to suspect that I disagree, but I don't take the bait... which seems to frustrate them, because they keep bringing this stuff up and I keep sidestepping it. It's like they're looking for an argument or at least a debate, which is not something I enjoy.
It might be time to make your response a little more direct. You could just say that you're happy for them, it's great that they're happy with where they are, and that you prefer not to discuss the specifics of your own finances... but hey, isn't this a great restaurant/beer/weather/whatever unrelated topic comes to mind? Or if they're REALLY good friends, you could just ask them, nicely, why they keep bringing this up and what they hope to gain from the conversation.