Well now. I'm pleased this subject garnered a bit of attention. To be honest, I expected no more than a comment or two.
This thread has splintered into multiple issues. Given the nature of this place that is unsurprising.
At any rate, I'd like to add a few comments on some of these matters.
I don't believe Gandalf "wanted" to enter Moria. I doubt that anyone other than a Dwarf would have desired to do so at that time. However, he clearly "felt" it was likely that the Fellowship's course would take them through Moria. As some have commented, perhaps he wished to evade detection for a time and take the road less travelled. I would like to suggest that, apart from his wishes and his strategies, perhaps Gandalf "had to" enter Moria. Great forces were astir at that time. All of the plans and courses of the Powers were coming to a head. Either Sauron would prevail, and all would become dark (until perhaps the Valar roused themselves and took a direct interest in Middle Earth), or the end of the "Elder" days was at hand, and the time of Man's dominion had arrived.
I know that Tolkien uses the term "Elder Days" to mean the First Age. I do not intend this usage here. Instead, I use the term to refer to the time that the ancient things and powers yet walked in Middle Earth and were not yet departing or waning to become the stuff of tales and legend. If Frodo suceeded in his quest, all such ancientry would be swept away as Elrond and Galadriel predicted. No longer would the Valar or even Morgoth and Sauron work their powers directly on the Lands of Man. In order for this to occur, one certain obstacle, a power from the forgotten past, had to be dealt with: the Balrog.
So perhaps, in order to fulfill his duties, and to advance the Quest, Gandalf was fated to enter Moria and slay the Balrog. He didn't want to do it. He "had to" do it, whether consciously or not.
As to the viability of routes other than Moria, even Celeborn criticizes Gandalf's choice. "Gandalf fell from wisdom into folly, going
needlessly into the net of Moria."