No, a 51% attack works 100% of the time. You may or may not win a single hash, but by 100+ hashes your chain is longer invalidating their chain. Further, if it looks like your winning people will defect to you're side.

> gold

Gold is actually used for a lot of things (ex: gold leaf on books), historically it's price has gone up and down quite a bit, but within a fairly narrow band. ~0.1x to 1x while being easy to hide or smuggle.

> probably drop

Even then it's still worth more than 0.

PS: In reality you would likely cause a fork, but that would also drop the price causing miners to migrate to some other coin making further manipulation easier.