I'm also looking into San Marcos, but an adult's vibe is definitely more of what I'm after. As long as it's a safe neighborhood, 20 min drive from beaches and nightlife, and has a private yard I could smoke my weed in peace in I'd be happy.
San Marcos is nice. You have a straight shot (its the 78, I think?) that goes right to Oceanside. Plenty of stores and all that stuff. Good choice.
I gotta defer to the folks that grew up in SD, I'm a transplant as well. Hope some information helps you