Some of your questions may be answered in this thread
http://www.hobiecat.com/community/viewtopic.php?t=9466
The differences in the hardware are pretty minor over the years. Very early Waves had the H14 style mast base, sometime later ('96 ish?) they began using the current H17 style ball/post base. Otherwise, the biggest change was made in 2005, bieng the new EZ Lock rudder/tiller system, using the glass reinforced nylon rudder housings. These are quite rugged and easier to maintain. This system also keeps the tiller behind the mainsheet as opposed to the prior H17 style rudder assembly which had the longer tiller arms forward of the mainsheet. Some changes were also made in tiller connector joints, some of the 'connectors had issues (tendon style), the current 2007 tiller connectors seem to be pretty trouble free.
As for play in the the hull/crossbar rig, you can expect some, even in a brand new one. They are designed that way for easy dissassembly. I would think if it were really extreme, (walk away) there would be some cracking of some sort around the crossbar sleeves, as mentioned in the above quoted thread. If the tramp is old and stretched, it will seem alot worse. If it is normal play, some of that can be improved by tightening up the tramp lacing. Not sure how to guage what would be considered unacceptable play, other than to visit a Hobie dealer and check out a new one to compare.
Good luck.