Along with all of the great answers above, as a space-faring fan I like the deal with blocking sunny radiation: http://www.geek.com/science/geek-answers-why-does-nasa-use-so-much-gold-foil-1568610/
I can't easily find the relevant ancient-alien-theory articles, nor do I take them all too seriously, but they show some nifty illustrations of how spacecrafts can benefit from being completely covered in gold. According to some theories the aliens only came to Earth for gold, and its worth was just that - coat-o'-gold for yee ol' spaceship.
Gonna paint my waggon, gonna paint it good...
And while you're off travelling the galaxy in your "check out my golden ship", don't forget to bring along some golden snacks: http://www.odditycentral.com/news/golden-kaiser-schnitzel-comes-with-real-gold.html
As for gold in a steel alloy, you're in for a disappointment. Modern steel doesn't corrode so quickly that it'll benefit much from a 1-5% gold infusion, and at the 5% mark I think you'll start seeing some softening of the alloy (which can be bad in big buildings, but some smaller ones might benefit from this.. it really depends on what you're building). Anywho, it'll be prohibitively expensive.
Besides, you won't have enough gold on earth to build much. You might consider using a pyramid to create extras: http://www.abovetopsecret.com/forum/thread1022234/pg1
Or just the neighbourhood nuclear reactor/accelerator: