I'm a huge fan. Some guys do upgrade the twin shock bikes with Prolink or 1100F swingarms and it's a nice improvement. JJam aka Jim Sawtell is an excellent resource for that as they need shock eyes welded on - it's a monoshock swingarm.
You should definitely avail yourself of the two main CBX forums, I help admin one of them.
http://www.cbxclub.com/forumand
http://www.cbxworld.comThey are both excellent resources.
As far as what year, that's a matter of spirited debate. The 79 is the first year, silver wheels, and a gnat's ass more powerful on a dyno on a perfect day. The 80 had something like 100 different improvements over the 79, including a much better swingarm and pivot, and there are far fewer of them. Those two are referred to as "twin shock" or "early model" bikes. I have 3 80s and two 79s. (How did that happen??)
In 81 Honda totally changed the bike, put a big sport touring fairing and slim saddlebags on it, and arguably created the first Japanese sport tourer. I didn't care for them till I rode one - it is in many respects a much better motorcycle: Mono shock rear, much better swingarm, 39mm fork (as opposed to the 35 on the twin shock), and a greatly improved (and quieter) clutch basket, among other improvements. A few guys make naked versions of those and those are possibly the best CBX of all performance wise, but they lack the classic appeal of a red twin shock, to me.
Go forth and browse young man! And ask away. I'm not the cat's ass with CBX knowledge, but the guys that are are on those two websites.
N.