Well mining uses hardware/electricity which has "real value". So you could say that 1 btc = price of electricity to mine said bitcoin. Now depending on what type hardware you're using to mine, it's anywhere from ~3 mhash/W for video cards to 20mhash/W for FPGAs to 90mhash/W for ASICs.
Story time:
Companies are usually valued by either their accounting profits, the cash they generate, or the value of the assets they hold. In some cases, where the company has no assets and no profits in the short term, it might even get valued based on their revenues.
Back before the Dotcom bubble burst, the financial markets were struggling to figure out how to value technology start-ups. They all had promising ideas that sounded like they could potentially earn an undefined large amount of money at some undefined point. However, without assets, profits or sales, investors and equity analysts couldn't figure out how to place a value on the companies.
Eventually, one method became popular and frequently cited in research reports:
Technology start-ups are worth a multiplier on invested capital. After all, since the idea is good, any money spent to bring it to fruition must create value, right? If the company burns $10 million per year in power bills, internet bills, office rent and salaries, it should surely be worth at LEAST $50 million in 5 years, right? In essence: The more money the technology start-ups spent, the higher they were valued. Companies were basically valued as a multiplier on cash burn rate.
We all know where that went. I'm not saying Bitcoin will go that way (although, as I've made clear here, I'm extremely skeptical and wouldn't put my money anywhere near it), but keep it in mind when you try to justify the value of Bitcoin by saying "it takes x amount of resources to create". Value is determined by demand, not by cost of production. Something doesn't get more valuable just because it's expensive to make.
Just like companies consisting of thirty cocaine snorting engineers with an expensive office and the world's coolest espresso machine wasn't worth anything in 2003.