There are three areas that are most popular (IMHO). In no particular order:
A) Downtown/Gaslamp/Convention Center, lots of very nice to medium quality hotels with amble parking choices. When you're not hosting restaurants, shopping, etc are walking distance. Waterfront locations but no beach.

B) Mission Valley/Hotel Circle. More inland, but all major highways kind of converge. Lots of hotel choices but IMHO discreet parking can be a challenge for your potential guests, depending on the hotel. The lower end hotels in this area attract a lot of low end providers. Plenty of restaurants and shopping nearby, but you'll drive from place to place.

C) Del Mar/Carmel Valley, just north of San Diego (20 minutes north of the airport/downtown). Fewer choices but nice hotels and resorts. When you're not entertaining a guest, the beaches are close.

I left out LaJolla (beautiful, but too hard to get in and out of) and North County Coastal areas (Carlsbad, LaCosta, and Oceanside) just because a lot of people think its "too far."

I can't help with your key card question other than it's more common downtown.

If you can PM, send me a message and I can offer a few specific hotel names that I like. I prefer not to mention them publicly.

enjoy your visit!