Are there any issues, generally, in a Prairie that surprised you and caused you to take a step back or wonder if some other model might have been better.
You didn't ask, but I'm another converted Prairie fan, so I'll take a stab at this too.
I think the biggest drawback to this boat is its age. A lot can happen in 37 years. Problems you find in a Prairie are going to be more a function of how well it was (or wasn't) maintained than original design.
Like any old boat, you'll want to check for port light and hatch leaks, engine condition, tank condition, hull damage, condition of running gear, etc.
As for the design itself, very few complaints. I think I'd like a hard top over the flybridge, and maybe even over the aft trunk ("sundeck" area.) I'd have accepted a few less gallons of water in exchange for a few more inches of headroom on the centerline berth. My own boat was over-powered by the original owner; I'd have gone with the stock engines.
The big flaw, and my biggest fear, is that the fuel tanks were completely bedded in foam. The foam will hold any moisture against the tanks, and they can rust. Replacing them would be a very major project which may not be justifiable cost-wise.
Another thing to consider with this style boat, regardless of manufacturer, is your agility. There are a lot of steps to get from any part of the boat to any other, and without a transom door and cockpit, even boarding can be a challenge to some.
Finally, soft chines on a shallow hull do allow this boat to develop quite a roll if seas or wakes are coming on the beam. Again, this is not unique to the Prairie, but more of a generic issue.