Hi Jamsmom,
Okay, I will attempt to answer your questions, hopefully someone else will give their opinion as well...
1. As a whole, discounts notwithstanding, WDW is more expensive. Mainly because DL does not require as much time. However, DL Hotel discounts seem to be a lot harder to come by than WDW and all the codes that they have now. The best I was able to find for my October trip was a DC discount. BUT, at DL, IMHO, it's not as important to stay "onsite" because an "offsite" hotel is literally across the street from the entrance. Staying offsite can also save a lot of $$$.
2. I feel safe at DL and the surrounding areas, but don't expect it to have the same atmosphere as WDW. We feel comfortable walking at night from DL to a hotel down the street.
3. As far as I know, there are no "common" towncar/limo services. The most common shuttle service (i.e. big blue van) is Supershuttle. Maybe a CA resident can shed more light here?
4. I plan to take advantage of EE, and have in the past. It's different at DL because there are only 2 parks, and DCA doesn't offer early entry. It's not like WDW where you have to use "reverse psychology" and go to a park without EE. At DL, it's pretty much use-it-or-lose-it! That being said, I think only Fantasyland and parts of Tomorrowland are open, so if you have kids, it's great, and you can probably catch Space Mountain a couple of times too. Plus, you can have breakfast there without rushing.
And no, there are no value resorts at DL. The lowest price I've ever seen for a
Disneyland Resort Hotel (there are 3) is $150, and that was a special price. Regular price is $200+. If you want value, stay at one of the hotels across the street. IMHO, it's nice to stay at a DL Resort Hotel, but it's not a "must" as in WDW (I'm one of those WDW onsite or bust people).
5. Knott's is pretty close, maybe 10 minutes away. Universal is 45 minutes to 1 hour, and Magic Mountain 1-1 1/2 hours drive, depending on traffic. And CA freeways can get pretty busy during rush hour.
6. DL and DCA can probably be done in 3 days. However, if you stay for 7 days, you can easily find other things to do in the area (see #5). If you go down to San Diego (1 1/2 to 2 hours drive), there are even more things.
7. Can't answer this one, we always have a car. However, I don't think there is a really good bus system there. Again, a CA resident could explain better.
8. LAX (LA International) is the largest airport, about 40 minutes to 1 hour away (depends on traffic), but Orange County (where DL is) has an airport also. You may need to see if your airlines fly there.
9. DCA is a separate park, so yes, there are 2, DL and DCA. I'm not sure what the closest water park is, I think it might be where Knott's Berry Farm is.
Good luck, hopefully you will get some other responses as well!