The truly rare, difficult and world-changing is the realization (production, enactment, what have you) of a really great idea, and the luck of that realization occurring in the right context.
Nonetheless that doesn't make the idea itself worth little (let alone nothing). By analogy, land is normally little use unless you put a building or infrastructure on it or start farming or mining it. And it's seriously expensive and difficult to do those things. But that doesn't make the value of land low. Land isn't just valuable, it's expensive in the most literal and straightforward you-pay-money-for-it sense, sometimes staggeringly so.
Land doesn't have any intrinsic value. There are two reasons (unused) land has value:
1) Someone expects to be able to use it to create value 2) Someone expects that someone else will want to use it to create value in the future and they expect that scarcity will come into play allowing them to charge more for it in the future than it currently costs to buy.
Land is only staggeringly expensive if either the value expected to be generated from 1) is exceptionally high or the expected value someone else will generate from it in 2) is exceptionally high.
If those aren't in play, you can get land very cheaply, or even for free, or in extreme cases be paid to take over land (that usually only applies for contaminated land etc).
Obviously ideas are less reliably scarce than land, because a number of people can have the same idea independently, and also because once another person hears your idea they can steal your fire without paying you, so it's difficult to trade an idea in a way that doesn't remove your ability to capture the value from it. But a high-quality and unobvious idea tends to occur to only a few people at any time, and the awkwardness of trying to do deals with them is far from rendering them valueless either. It's certainly not the case that good ideas are plentiful in the sense that if there one specific good idea to solve your problem but you don't think of or hear of it, then don't worry, there are lots of similarly good and suitable ideas lying around and one is almost certain to come to your attention soon.
A different, and notable distinction between land and ideas is that people are usually better at recognising valuable land than good ideas, as Frank Aiken observed https://en.wikiquote.org/wiki/Howard_H._Aiken . This is one reason why some ability to "finish" (in terms of external circumstances as well as internal factors like temperament and character) is such a valuable accompaniment to having a good idea: it helps to have something relatively tangible (be it only a prototype) to force down others' throats.
It wasn't very brilliant then, was it?
Even ideas as earth shaking and complex as Infinitesimal Calculus and Quantum Mechanics were developed in parallel initial by people with little to no communication between each other.
It's not quite a "no true Scotsman" since great ideas do happen and happen fairly often, in the grand scheme of things (there are over 100 Nobel prize nominees every year). The oft-repeated argument about ideas versus execution is that ideas are a dime a dozen, which is true, but most of them are not really all that great or original. The same can be said for any resource.