I'm in the same boat as you... looking for that family sailboat <$50k. You can do pretty good on a mid to late 80's 30-34 O'day, 30-34 Pearson, maybe the 33 or 34 Tartans. But for a family of 4 I think getting a 30'-34' would be ideal, especially if you'll be doing long weekends and that annual week long trip.
Here is a 1988 two cabin layout 33 Pearson, also has the aft head which really opens up the salon.
1988 Pearson 33 Boat For Sale
Also check out the 31' Pearsons, cica 1987 to 1991. Not two cabins, but a nice boat with a lot of room.
Dr. B makes a good point too on a boat from the 80's. It really has reached the end of its depreciable life, so you shouldn't lose too much money on it if you buy smartly.
Good luck and have fun looking for that perfect boat.