I've used that manual almost exclusively, although I did buy two other Haynes manuals recently, for suspension/drivetrain and heating/air conditioning. What I haven't learned from that J-Series manual, I've learned mostly through this website, although I've been working on cars and other mechanical stuff since I was a kid. (The only things I'm still lost about are welding and working on automatic trannies.)
The main thing is to be fearless about your ability to do a particular job. If the meatheaded grease-monkeys at your local garage can become certified mechanics and charge $50/hour, then you can at least learn to work on your own vehicle.
P.S. This '88 Grand Wag is by far the most difficult vehicle I've ever owned in terms of working on it, largely because of the lack of room to get to things, and all the emissions junk and vacuum lines that are a pain to keep working properly. I had a '79 Ferrari 308 GTS for a while, twin-cammed and with three 2-bbl Weber carbs -- by far the easiest car I've ever worked on (except tuning those carbs was tricky). Those Italian guys knew someone would have to work on it eventually. In contrast, I think AMC/Jeep planned for their upscale customers to return to dealer mechanics, so they could keep up with all the recall notices!
[This message has been edited by Ralph (edited July 20, 2000).]