I'm a born and raised St. Louis girl (I used to work at The
Disney Store in Chesterfield from '95-'98), so I know her predicament and can give her some good comparisons for her questions. Everyone in STL goes to Orlando. Just the way it is. I bought DVC when I lived there and we went to WDW at least 2 times a year. I moved out her to Los Angeles 8 years ago and now we are at DL about every two weeks. I would defintely come out here to DL. I think the younger folks in the group might like to do the "hip thing" to come out to LA, the OC, and the Hills and hang out like a movie star. How often do you really get to do that?
Driving here during the day is about like driving on I-40 from Downtown to the Interbelt at 4:30pm. Rush hour is like leaving downtown and going over the Poplar Street Bridge in a mix of rush hour and after a Cards game. You basically want to avoid being on a freeway between 7 and 10 and 3 and 7. Saturday traffic is still like an easy STL rush hour - crowded, but moving. Sunday morning are the best. Like I-270 during the mid day. My SIL won't drive here. My brother does it begrudgingly. I give them directions, because MapQuest doesn't allow for traffic flow and always wants to route them through downtown.
Orange County/Santa Ana/John Wayne (SNA) is the closest to DL and before American's departure as a hub, had 4 nonstops a day. No longer the case. LAX might have a better non-stop or either American or Southwest for you - it's a 4 hour flight on the way here and 3.5 hours home (I did it every two weeks for 1.5 years before I moved here). Either way, the drive isn't bad in a rental car. The freeways from LAX to Disney all have carpool lanes, so that cuts down a little time. If you don't want to do the car, then take the Gray Line Disneyland Express bus. Fast, easy, cheap! Straight to DLR in comfort. You could always take the bus and then get an Enterprise rental car delivered to your hotel on the day you want to go explore!
GCH is the coolest hotel (with an architecture tour every afternoon and you don't have to be a guest), but DLH has the better pool with a great slide. You can also get some nice lock-off suites in the Wonder Tower, where you have two bedrooms (one is a king suite with queen pull out in the living room and the other is 2 queen beds) where everyone can hang out. They may have these suites in the other towers, too, but I have only stayed in the Wonder ones. Not sure what PP has to offer, except an excellent breakfast buffet!
It's a 5 minute walk from the DLR hotels to the park plaza - go through security and look left at DL, look right at DCA. The entry gates are about 1000 feet from each other. Makes park hopping a breeze!
We have a nice weather phenomenon in June called June gloom. It's cool and slightly overcast with no rain and no humidity. VERY pleasant time of year to visit. With a group that age, you can do several days in the park, then take time to drive to some unique sites, like the surfing and shopping mecca of Huntington Beach or go see the unique sights/freaks/muscle men at Venice Beach with a quick pop over to Santa Monica (3 miles away from Venice), Rodeo Drive (15 miles inland), or Malibu (just a bit further up the coast) for some shopping and/or celebrity watching. There is also a new shopping/dining extravaganza that just opened up in walking distance from the DLR called Garden Walk.
If you really want to do Universal, it's VERY different than the Florida park. The teen group you have would like Universal. The park is built onto the side of a large hill, so you have escalators that take you to different levels of the park. The set rides, like Earthquake/Disaster, King Kong (which burned in the fire), Jaws and such are part of the tram excursion, so you don't have separate lines for those. Citiwalk is very nice - some good restaurants, too.
Universal really is a working studio (had friends that worked on productions there). They film all of the time, but certain times of the year see more work than others. Television shows and celebrities actually have summer vacations. Thing is that June/July really doesn't see much filming work - shows are on hiatus and most movies are usually in post production at that point, so the backlot is a bit dead. The fire has also closed some of the backlot -several shows and films had to move production because of it.
Best studio tour is actually the Warner Bros. Studio Tour. They are down the hill from Universal (less than a half mile from Universal's back gate to the employee entry gate at WB). They have a tour where you get on large golf carts with a guide and really tour the entire lot. During the down season, they will let you get off the cart and go onto soundstages where TV shows actually film. They even have a great museum on the lot, with amazing displays of historical items and a wild Harry Potter exhibit upstairs. This is not available for the general public, only employees and tour guests. They closed the lot to us family members after 911. Last time I did the tour with a visiting friend, we saw them shooting a scene for Gilmore Girls with Alexis Bleidel and I also caught George Clooney taking a break outside a soundstage while doing some additional scenes for Ocean's 12.
Of course this doesn't even cover our other cool things like the Wilshire Boulevard attractions like the La Brea Tar Pits, which is next to LA Co Museum of Art, and across the street from the Petersen Museum of Car Culture - possibly one of the coolest museums I have ever been to and I don't even like cars that much. Rodeo Drive is just 15 minutes straight down the street from there.
These are just some other things to do while here. Or, you could let the kids go wild on their own in the safe confines of WDW, while you hang out. Both have benefits! I'll stop now. My novel is mostly done!
Nancy
We went together to DW in '07 and now we are going to DL in '09. My immediate family has been to both since we are DVC members. I thought I was not going to enjoy DL as much as DW and boy was I wrong. Yes, it is not as large as DW, but there was so much still to see and do in Southern CA, besides DL. And the weather in CA cannot be beat in June if comparing CA to FL. At DL, I even think, some of the rides were better then the DW version. We also love the history and love that Walt put into DL. So I don't think you could go wrong whatever you pick. 
