Whether or not Lucas takes his own movies too seriously is an open question, but it's interesting to contrast Lucas' career with that of the Wachowski Brothers, who crafted The Matrix and its ill-begotten sequels. Regardless of whatever kind of philosophical or mystical mumbo-jumbo may have been sitting on the wings, Lucas takes great care to make his movies, all his movies, wildly entertaining. The Wachowskis, after the release of the first Matrix film, were faced with the daunting challenge of crafting a movie trilogy which most were comparing - the second two films sight-unseen - to Star Wars. As everyone knows, they blew it. Not even the most hardened cyber-partisan could view the second two Matrix films as anything other than shambling messes punctuated by occasional bits of gorgeous imagery. (The fact that they were still quite successful - albeit nowhere near as successful as they would have been if they were any good - says a lot about the unrelenting mediocrity of moviemaking in the 21st century.)
The Lucas of 2005 knew the same thing that the Lucas of 1977 did, which is that at rock bottom you have to have an enjoyable film, or people just won't care. The Wachowskis put their cart before the horse by crafting a nonsense philosophical manifesto and then bolting a movie series around it. It's interesting to note that both Lucas and the Wachowskis fell into problems for similar reasons (although Lucas was able to extricate himself with far more equanimity): neither Star Wars or The Matrix were initially pitched as self-contained trilogies. Both were single movies that became trilogies by way of their unanticipated success. Lucas was able to think on his feet fairly well, but there are enough inconsistencies in tone and theme between the films of the initial trilogy that it's easy to imagine that A New Hope would have been a far different film if he had known he would be saddled with these characters and this universe for the next six years, let alone three decades and counting. (As it is, A New Hope seems to exist apart from Empire Strikes Back and Return of the Jedi, the latter two essentially one long story, whereas the first movie was complete in and of itself. Lucas would return to this structure in the prequel trilogy, with The Phantom Menace acting as a kind of self-contained prequel to the prequels.) Taking into account the numerous discrepancies between the later films and Lucas' own novelization of A New Hope, along with early artifacts such as Alan Dean Foster's Splinter Of The Mind's Eye and the regrettable 1979 Christmas special, it's easy to see that the "mythos" took a while to develop.
These inconsistencies in tone are almost entirely absent from the prequels. What few unfortunate moments there are occur seem to occur almost exclusively as a result of Lucas changing the shape of the movies to fit the preconceptions of the fan base who wanted the movies to be something other than what they were obviously designed to be. The fact that the origin of a minor character like Boba Fett featured so prominently in Episode II pointed to decisions made not necessarily for the health of the picture but to appease an unappeasable fanbase - could any uninterested observer, having seen the original films but nothing else, have reasonably predicted the prominent role Fett would play in Attack of the Clones? Also, the fact that Jar Jar Binks, despite his significance to the plot, plays a far less prominent role in the second film than the first, and is entirely absent from the third, implies that poisonous fan reaction took its toll on Lucas' better judgment. It's common knowledge that most people don't like Jar Jar, but writing out the character simply because he proved unpopular bespeaks a regrettable loss of nerve on Lucas' part. Perhaps I was the only one, but I was sorely disappointed to see Jar Jar missing in action in the second two episodes. (Hopefully the forthcoming television series will remedy this exclusion by showing us more of Jar Jar's adventures in the intervening years.)
In retrospect, the original films suffer for their tight focus on a small set of central characters -- an unfortunately aristocratic reaction to the challenges of filming a massively broad and essentially sui generis epic the likes of which no one had ever really attempted before. (The scale of world-building on display was unprecedented, and while many filmmakers would attempt to duplicate it in the years that followed, few would succeed.) Many of the emendations that Lucas has subsequently perpetrated on the original series have been conducted with the express purpose of pulling back the tight focus and inserting more of the truly cosmic scope that pervades the prequel trilogy. There is no way that Star Wars fans will probably ever warm to the "Special Editions", and in their defense there really isn't any reason they should have to. The original three movies are unique and special for many reasons both nostalgic and historical, and by tampering with them Lucas was admitting his dissatisfaction. He should allow the fans their memories of the original trilogy, while taking deserved pride in the fact that the prequel trilogy is the most perfect reflection of his ideas possible. (Whether or not those ideas are any good is, of course, in the eye of the beholder.)
With the creation of the prequel films - and regardless of their relative or perceived quality - Lucas has stepped into the ranks of the most exacting auteurs in the history of filmmaking. The fact that he enjoys practical and absolute authority over his productions, from every step of financing to the creation of the entirely digital environment in which his characters interact, might just make him the single most powerful filmmaker in the history of the medium - it's odd to imagine a hypothetical Hitchock in the age of pixels and CGI, but it's hard to argue that he wouldn't have embraced any techniques that would have maximalized his control over the finished film.