I've played the Concierto de Aranjuez with orchestra several times. I preferred to get my scale technique to certain level before taking on the music. Once that happened, the piece flowed quite well.
I know this probably touches on the eternal debate of whether technique is "developed solely through music" or not. While I certainly believe that certain types of technique can only be developed by playing literature (usually the more refined aspects of music making: voicing, tone, legato phrasing, accuracy), if one attempts things for which one isn't properly prepared, especially a basic technique like scale playing, problems can ensue.
One's ear can become fatigued through all the effort and repetition required, which might render the piece dull and lifeless. And if technique is the primary concern, there's no mental energy left to devote to artistic issues. And to my mind this separates technique from music as much as the dry pedagogue who can only talk about finger movements and fails to see the larger artistic picture.
If dk's example of a guy who practiced the piece for five years needed that time to get to the point where he could get through the piece, I'd say there's a big problem. If, on the other hand, he was using that time to generate creative musical ideas and refine his interpretation, that's a different story. The legendary pianist Dinu Lipatti was once engaged to play a Beethoven concerto. The conductor said, "Great! When can you do it?" Lipatti said something like, "In five years," (perhaps it was three). In Lupatti's case he wanted the time to grow artistically with the piece.
For myself, I have found that speed, so necessary for the Aranjuez, comes fairly easily as a result of the quality of my basic technique. But if I simply try to increase the quantity (i.e. speed) of a technique that has basic problems (say, a bad hand position or a tense movement), I'm in for trouble. The big trick, of course, is knowing what constitutes quality.
That said, certainly a phenomenal piece such as the Aranjuez can inspire all of us to work hard (and smart!) on our guitar playing!