Seven Seas is easily walkable to town - we've frequently just strolled down the beach - call it 5-6 blocks. Papi's Diner is right behind Seven Seas and La Popular Bakery is only a block or so away.
All of the best snorkeling spots are along the reef, which requires a boat trip. You can snorkel off some of the piers around town, but, they're not like the really great spots. Carol at the front desk of Seven Seas can help you arrange the snorkel trips - I recommend 'lil Alphonse - and the guide will pick you up right on the Seven Seas' dock.
It's been a year since we were back in San Pedro and that's about 11 months too long - enjoy!