As long as you're not reckless with your 3DS, you shouldn't have to worry about it. I can't imagine what scenario you could really be in where it would snap in half WHILE you're using it. Just make sure to fold it up and put it someplace safe when you're not using it and the durability of it should be a relative non-issue.
As the sound... the sound quality of my 3DS XL is actually pretty good. Sure if I'm playing it while out and about I'll use headphones, but sometimes if I'm just sitting alone at home, and there's no noise around me, I'll play it from the speakers. Headphones can be uncomfortable. Earbuds can be a nightmare if you have them on for too long, and regular headphones can be clunky if you're trying to get comfortable and play at the same time.
I'll give you that the speaker issue isn't a deal-breaker by any measure, but being able to get good sound quality without headphones is certainly a perk.
As for the layout, I can't speak from experience, but from what I've heard the main issue most people have is that while its fine using traditional controls, if you need to use the stylus while playing, it can get rather uncomfortable.
The 3D feature is somewhat similar to the speaker issue for me. If I'm out and about on the road or something, yeah, I'll turn the 3D off to keep the battery going longer, but when I'm home and near a power outlet, I actually really like the 3D. I didn't think I would, honestly, and was considering getting a 2DS instead, but after playing it with the 3D on, I'm really glad I went for the 3DS XL instead. It may not be required for games, but it looks damn good on the games I've played. And as for the power with the 3D off, even you admit the difference isn't that huge.
Simply put, I would say to go ahead and get the 2DS if you're in a situation where you think you break your 3DS... like, for instance if you have kids and don't have any place to put the 3DS where they can't reach it. Really, the increased durability was intended as a safety measure for children, as... well, kids do have a tendency to break things.
If you only play a handheld while you're out on the go, and you don't mind always having to carry around something big enough to store the 2DS in when its not in use; and you don't mind not having the option to use 3D, then I suppose I could also recommend the 2DS. But even then, I would kind of be leaning towards one of the 3DS models, just because its so much simply to be able to just flip it closed and stuff it in your pocket when you're not using it; and there's the added bonus of having a more comfortable layout while using the stylus.