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Nowadays it is trendy to have the best presentation in restaurants.
Nothing wrong with it. But when my butter has to be "introduced", it is just too much.
In the end still good quality food and reasonable price sell.

I do agree that food quality is most important AS LONG as decor is not downright bad (simple, even old is OK, dirty isn't, in my opinion).
I also agree that a new restaurant might be better-off by starting to concentrate on the food quality than decor, but once established I think it can be good to improve decor if the food doesn't have to suffer.
I don't see how "Spending on food (...) may not be necessary", what are you thinking?
I think some restaurants may, in fact, be more about the experience/decor than about the food and people may know that when they go in... look at the jungle-themed chain(s).
Without being a critic, I enjoy both food AND service in some places, like Benihana, Japanese Village and other such themed restaurants.
All in all, what you say may be true for most people/restaurants, but with some great exceptions

Do you think too many restaurants spend too much on décor and not enough on food? I certainly do
Restaurant business is tough. Everyone knows it. It is probably difficult to have money for both. Many owners likely have to compromise on one and sadly so often it was food.
Why it is a bad choice?

First of all, you are spending up front a big block of money for a potential profitable business. Please read about the failure rate of any restaurant. Spending on food is gradual and may not be necessary.

Secondly, with fancier décor people probably expect better services and large menus.
better services = more expense for owners
Large menus lack focus and takes too long to order which reduce the turn around rate
Yet - YOU STILL CAN NOT PLEASE EVERYONE.

Thirdly, "word of mouth” marketing nowadays is more important than ever since we are in the social media age. If you ever noticed, People’s reviews are more likely focused on food rather than anything else. Surely sometime you see some remarks on services and décor and it is usually either neutral or bad. Why? maybe how we want to be treated is quiet subjective. Maybe some people just want to be left alone. But good food, we seem to have relatively similar ideas, don't we? Salty, greasy, burnt are probably no no for everyone!

Lastly, Food will be essentially what drives customers back to your place again and again since they saw your décor already. The cost of attracting existing customers is only a fraction comparing to new customers. You know what I mean if you track marketing cost closely.