Your first point is spot-on: Everything has only as much value as someone else is willing to give it. US dollars have their value because someone is willing to have them instead of whatever product or service they're providing in the meantime. In this sense, gold has no more or less intrinsic value as any monetary system anywhere.

There is, however, one way to universally devalue any resource, and that is simply to either make or discover more of it. Regardless of its initial value, making more of something simply makes it easier to come by, which in turn ends up making it worth less by those who trade it.

The problem here is ultimately one of control. It's true, on a gold standard, we have no control over the supply of gold, although we do know there is only so much in the entire world. Any discovery of a brand new set of veins would cause fluctuations, possibly significant ones, and they would be at somewhat random intervals. Someone (or rather, a number of people) control the US dollar, since they are able to determine how much to print and how to distribute it. Of course with this come all the problems of a manipulable resource. By printing arbitrary amounts of money, the controllers of the US dollar can implicitly tax everyone who deals in that currency by printing a lot more money, thus watering down what is already out there. This is one example of many which a controller of a currency can do to manipulate its value.

Really the question boils down to this: Which is better, a currency that cannot be controlled, or one which is controlled by people we cannot necessarily trust? I have my opinion, and I'm sure you have yours, but in either case, this is the question you must ask.

Finally, I must disagree in part with your final comment. You would be right in recent years that there would still be inflation, since a great deal of that was due to loans being made by reserve banks, which increases the perceived amount of money in the world, and thus reduces its value. However, this inflation trend is continuing in the wake of people defaulting on loans. Each default should cause the perceived amount of money to shrink, ultimately causing each individual dollar to be worth more. However, this isn't the case right now. Inflation is high, and apparently still increasing. I can't help but think that this is, in part, because more money is actually being printed in order to help the banks in the reserve system. But whatever the reason, a gold backed currency (if actually backed) would help prevent the current stagflation which is occurring right now.