Do it. (go there that is)
Last time I saw La Vuelta was Navacerrada in 2003, it was great to be there about an hour before the riders came through – it's awe inspiring to see the effort on their faces and to see them hooning up the climbs. When I went it was in the third week of the race and at the end of the season, so the aggression still being applied was amazing to see. As a bonus, we saw the incident that led to Manolo Saiz being chucked off the race for trying to force a tv moto of the road!
Of course you will see the race better on tv, but you'll get a totally different experience going to the roadside. You can always watch the tv later.
Ok, so that's the why.. the how? err, dunno, one thing I would say is that it might not be that busy as La Vuelta isn't as packed out as the tour de France is. So maybe you don't have to get there too early and do a) Mind you, it might still be a few too many proles for a Don, I don't know your tolerance levels. The fans were great imho. Quite the family event, I liked the lagered up guys with their regional flags – for the most part they seem like happy drunks in Spain.
So, worth it in my opinion, so very worth it. Put your pics up here if you do go.