The NADA values are notoriously low. If you can find any trailer at those values that hasn't been totalled in a wreck, I'd be surprised. In my opinion, an '89 32' could be worth anywhere from maybe $8000 to $16000 or more depending upon condition and options (things like window awnings, front rock guards, and solar panels, add value). From your description, I'm going to guess the one you mention should not be on the upper end of the range. A regularly used and maintained trailer can often be in better shape than one that has sat a long time.
It mostly comes down to condition. If no significant frame rust (check inside the rear bumper storage compartment if it has one), no signs of current water leaks or significant floor rot (all Airstreams will eventually leak, but that's not a problem if discovered and taken care of promptly), if all systems and applicances work (water, electric, fridge, A/C, etc.), no significant dents or extensive clear coat fading or peeling (some fading on top is to be expected in an Airstream of this age), and the interior is in reasonable condition (carpets, upholstery, cabinets, curtains, etc.) I'd guess the trailer could be worth something in the $10,000 to $12,000 range. Any problems found will start detracting from these values. An exceptional and highly optioned trailer could bring more. But don't take my word for value. A knowledgable person needs to thoroughly look over the trailer to really make a proper valuation.
Of course, depending upon the knowledge level of the seller, the NADA value could be a bargaining tool. Just remember that a knowledageble seller will know those values are low.
Wally Byam Caravan Club International Historian
Vintage Airstream Club Historian