What you're saying makes complete sense, but at the same time, I'd rather have the revision be a meaningful upgrade with content standing behind it than a minor facelift that doesn't bring anything new into the picture. Exclusive content is that meaningful reason to upgrade to the "new system", because really, when we're talking about doubling the computing power and memory, it's hard to call it a "revision". I don't think the old 3DS has nearly enough juice to pull off the likes of Xenoblade Chronicles (as much as I dislike the game) and even the New 3DS is stretching it, but it's definitely more well-suited for the job.
If we're talking about the N3DS in relative terms, it's still a very weak system specs-wise, but it is comparatively stronger than the old 3DS and it totally makes sense to trade in your oldie for a new model. The same is happening in the smartphone sector - phones get moderate upgrades every now and then and it's up to the user to purchase the new models and take advantage of the additional computing power and features. You don't have to upgrade, but you can if you want to.
The reason why Nintendo's consoles get such significant updates and stopgap systems is that Nintendo systems are just weak out of the gate and can't possibly remain relevant for a complete generation, it's been like this for years, although nowadays it's much more obvious. Is it okay to do? It depends on how you look at it. Sony portables don't have this problem for instance, but they're usually much beefier on release date and simply "last longer" in technical terms.
I really think that this is mostly a problem of specs inadequacy and that inadequacy springs from Nintendo wanting to push their systems at the lowest possible RRP. The problem here is that it's not the 80's anymore and mobile technology is developing at a very rapid pace - unless you release something that's mid-to-top range out of the gate, it's just not going to last for more than 2 years - it's how the cookie crumbles. Nintendo chose the path of periodical upgrades rather than releasing expensive consoles and lowering the price as time goes on and as such you're getting the stopgaps. To stimulate selling said stopgap systems, they release exclusive content for them - otherwise they'd be completely meaningless.
1. The reason even the New 3DS "struggles" with Xenoblade, has nothing to do with CPU cores and RAM amount (the things New 3DS improved). The GPU is the culprit (GPU is the same in both handhelds. Not even a mild clock boost). As for the resolution downgrade, it is obvious it is a matter of screen assets as well. The point is that the bottleneck is the gpu and the screen resolution, and those are the same in both models...
2. While the New 3DS is arguably a new console with backwards compatibility, since not only it has new specs but also exclusive AAA games, it is not a true successor. There is a reason we have "console generations". Note that we don't have "PC game generations" or "mobile game generations". Only consoles. The reasons for this are for another discussion, because it will take long... But what matters is that when you blur the "console generations" by releasing new consoles in the same generation, you destroy the very concept of gaming consoles, and make their point moot.
Notice how, in every article of Consoles vs PC, the main argument in favour of consoles is that you don't have to get new hardware for many years. The MAIN argument.
3. When you buy games for a smartphone, you can play them on any future smartphone. It is the same like the PC. You can upgrade your hardware and your experience how many times you like, but the software is the same and it carries over. Also, mobile environment is not a closed ecosystem, you can do what you like with your devices, and they are multipurpose.
On the other hand, you pay a reduced amount for a Console (or a hefty premium in Nintendo's case) hardware, in order to be able to do only what they like with this hardware. It is restricted and they control the terms. This is no smartphone.... The only reason to put up with this, is because there is an implied agreement that you are going to get support for the thing for a considerable amount of time. That is why you put up with the closed garden, restriction of the hardware functions, and higher game prices.
To put it simply, smartphones and consoles are different concepts, and you cannot justify what Nintendo did by saying "smartphones do this too". Because if Nintendo tries to copy smartphone concepts, it will destroy the barrier that separate the two, and in terms of price, performance, ease of use, and freedom, there is no comparison...
4. Nintendo releases weaker systems because it can make much more money that way, and it removes the incentive for western developers to compete with them on software. Notice that developers outside of Japan (and some japanese too) completely or almost completely abandoned Nintendo since they started this practice. Nintendo wants to profit both from consoles AND from software, and they don't want other developers to compete, because "it will lessen their brand".
Imagine if games like Skyrim were on Wii U: The new Zelda would become just a lesser Skyrim clone, and fans would go "meh". But now, after having them starved for AAA games and concepts like true open world gameplay, they will swallow Zelda and preach globally what a great game it is (because that is all they get to play).
The thing Nintendo doesn't accept, is that both the Wii and the DS were flukes. They arrived on a perfect storm, and selled far more units than they should. This won't repeat. Even the 3DS is not a success, because game attach rate is quite low. There are 50m 3ds consoles out there, but NOT 50m 3ds GAMERS. Most consoles were bought by previous 3ds owners because they wanted "to upgrade". This way they skew the true success of their consoles.
Nintendo with this kind of practices will keep shrinking, until they become the new NEO GEO. I don't believe they will become the new SEGA, because SEGA had the sense to go software only.