Now as someone who owns both, you need to realize as you said though the wagoneer was outdated, and chrysler didnt make the ZJ grand cherokee it was developed by AMC.. AMC btw didnt make the wagoneer. The wagoneer was made by kaiser.. So you see what im saying here ?
AMC bought kaiser.. they inherited the wagoneer, Chrysler bought AMC, they inherited the wagoneer and the ZJ development. Chysler actually improved on the wagoneer. Your wagoneer isnt the years that are sought after.. The Wagoneer that people want are the 89-91 years. Those are the Gems and guess what these are the chrysler years, they have better everything, they changed the starter, the A/C compressor they fixed the electrical problems AMC had for the most part, they added a rear wiper lots of other things improved under chrysler, the 4WD system was better. your 84 you have to stop pull the lever then flip to 4wd.. i can flip the 4wd lever and go right into 4wd at 50mph.
The ZJ was also a really good SUV, they just had transmission issues, and thats because people didnt follow intructions.. the transmission needed to be serviced every 24-35k depending.. and no one did that so after 50-80k miles people had dead trannies and thus the myth of shitty transmissions was born. The ZJ was one of the best years for grand cherokee's and that because it was developed by AMC and improved on by chrysler... after that the Grand cherokee became a chrysler only jeep.