There were only small alterations made during the first generation of the Amigo. In 1992, 4 speed automatic transmission was added for the first time. Some power options were added for the 1994 model year.
The Amigo that was introduced in 1998 was very similar to the Rodeo. The Amigo was shorter and had a stiffer frame. It was basically a Rodeo but for people who wanted more sport than utility in their SUV.
The new Amigo came with a soft top, which made it clear that it was competing for the same market as the Jeep Wrangler. A hard top was optional.
After much complaining from customers, Isuzu made a V6 engine standard on the Amigo. The earlier Amigos with a weak I4 engine should be avoided. Don't be fooled by the Amigo's small size, it weighs over 2 tons. You need a bigger engine in these vehicles. Remember this if you're buying one used.
You can find these listed on eBay, although they are not very common. You might also find a decent number of parts, as you'll probably need them if your Amigo has a lot of miles on it, which is should by now.