Yes, they do rehash, but rehash is not an inherently flawed thing and typically the issue I feel is people instantly go defensive about anyone saying this about Nintendo when they don't really need to because it's not an insult. A rehash does not mean 'bad', it just means re-using ideas without significant change, the significant part being the key offender here which people miss out, and anyone who says Nintendo does not do this is letting their affinity for them cloud their decision.
New Super Mario Bros, New Super Mario Bros DS, New Super Mario Bros U, Super Luigi Bros, whatever they're all called. Then all those previous games those games are based on. How many times have we got the hookshot in Zelda? The boomerang? I could go on and on. And people will argue that they still change their uses around and do new things with them but this content is still constantly re-used and the definition of a rehash, as I said, is something without significant change, and Nintendo's franchises are absolutely littered with things that fit that description, most of them at their very core. The hookshot between OoT, MM, TP, and SS may have had some different uses but it was still the same item with the same basic premise.
So once people get out of their heads that rehash is an inherently bad thing, then we can have a mature discussion about it and yes, I do think many Nintendo games are rehashes. There's been some change, but most games still follow almost point for point, as if Ninty's developers have a list of things they must include, the same basic point and premise. Nintendo's games arguably have more quality than a lot of even younger titles but they still ride the same franchises and the same formulas and just changing a few things up here and there. Probably because they don't want to rock the boat, afterall why would they, and fans don't want them to either, so I'm not knocking it. Objectively, at least.
As long as their games are selling and as long as fans want it, well, they can rehash all they want can't they? Many franchises rehash, it's kind of what they have to do, keep the same feel but still be creative and innovative with each iteration. As long as brand new content over-shadows rehashed content, it's never really a problem. Rehashing provides consistency and stability of a franchise's core gameplay but doesn't inherently throttle creativity within the game too. It's only when it all begins to stagnate and comes to a big full-stop that I feel it's really a bad thing and rehashing becomes a problem. Some people don't mind that, some people just want more more more and they're entitled to it, and the industry are entitled to provide for them as long as they do want it. Call of Duty is a prime example. People hate on it but people want it, so why shouldn't Activision keep making it? But it's when creativity and innovation is starved and the excitement is gone that rehashing finally becomes a bad thing, and that's when scores drop and sales die and then the franchise either needs to really re-invent itself or finish. A good developer will stop or re-invent the formula before that point ever hits, though.
So my conclusion is yes they are rehashes, either as a whole or constantly re-use many of the same elements from previous titles, but that alone does not mean they are bad. Skyward Sword, for instance, I thought was a bad game period. I did not think it was bad just because it re-used old ideas, I just thought it was a bad game for some poor design decisions and more. I may personally feel the rehashing of content has made me grow a bit bored of some elements of Nintendo's games, but if the fans want it and they're still selling then I'm definitely not knocking Nintendo's strategy. However, other publishers manage to still push out the same games while also having time to create new franchises too. I feel Nintendo needs to invest in the latter, and set their A-Team of devs like Retro off the lead and let them go wild.