Rincon Inn is fine, though the Hostel part of it gets packed. Economy rooms are good, but no window so it can get a little warm (even though they say AC, PR electricity isn't always reliable). I never stayed there but have friends who have and they never had any complaints. Not a luxury place, but good enough when you're gone every day.
One of the most important factors when planning a PR trip are the cold fronts. I use a floating date for the whole month of Jan every year. This allows me to time 2 solid swells EVERY time I go down for a 10 day stay. Your crazy if you just pick a date right now in Dec. It is entirely possible that Rincon won't break for a week. I would rather pay $100 more for a ticket bought late to ensure I get 2 swells in than sit around in Rincon only to have to drive north for wilderness or choppy jobos. Timing wise, when a low leaves hatteras the swell generally arives 2 days later and lasts for 3-4 days. Been doing this for the better part of 10 years and I always score propper. Float your date if you can. Trust me.