Mic, is it dark at night? Absolutely. The 1973 Z1 is the most valuable, but the Z1A and Z1B are very collectable. The KZ900 was born in 1976. All are nice bikes. A nice condition 1974 - 1975 could bring $4~8,000 easy. A fully restored one could go $10~12,000. I helped a friend of mine buy 2 just this week. A non-running bike with wrong paint, seat, and pipes still cost him $2,000.
Go for it. The bike is DOHC. Stock they made 81 hourse power, they are a bit heavier on top than the CB750, but really run for ever like the Hondas.
Hoped I've help you make the leap... Seriously, if you don't "junk" it up, cut on it, or drastically cheapen it, then every cent you spend on it will be returned when you sell. It's one of the few bikes out there that will continue to go up in value. I'm affraid the CB750's (non-sandcast) are just too available. Honda made over 60,000 a year for 10 years.
Regards,
Gordon