"Off-site" has a different meaning at DL than at WDW. There are many inexpensive hotels you can stay at "off-site" that are literally a 5 minute walk to the front gates of both
Disneyland and California Adventure.
We've never spent more than one full day in the park on our DL trips, though you could definitely spend 2 days at DL and a day at CA.
I love DL and have visited at least 10-15 times in the past 30 years (I'm 34 now) and just visited WDW for the first time this past May. I still love DL, but it just can't compare to the variety of parks, resorts, etc. at WDW.
So yes, you should go to DL, but spending 5 days there really might be too much, and don't expect it to be like WDW.
Tips if you decide to go:
If you've already seen Fantasmic at WDW, skip it at DL. It's still a great show, but it doesn't have it's own arena or seating so it's incredibly packed and people sit or stand on the ground.
Go on Indiana Jones Adventure. It's similar to Dinosaur, but a different experience.
Go on the Matterhorn.
Go on POTC (it's far better than WDW's version)
Go on HM (not better or worse, just different)
Eat at the Blue Bayou.
Go to Toontown (much bigger and better than WDW's)