Holy S&^% batman, 23K for a ZMR! If it doesnt have 60k plus miles thats an awesome price. Im guessing this is in the States. But have you ever seen a Roadster with the removeable hardtop? - Still has the lack of room issues but if you like the lines, buy the Roadster now and take your time chasing down a top.
http://www.zpost.com/forums/showthread.php?t=506391
http://www.zpost.com/forums/showthread.php?t=506662
Im guessing you are not buying this as a DD. If you are going to track it eventually then the coupe is the way to go, and you wait till you got the cash. It is always good to get what you really want, if you can afford it. The ZM's are great bang for buck right now, many low mile cars out there. Look at the cost of ownership as well though. If $4K is a deal breaker, hope you are a good mechanic with resources, these cars are not the cheapest to own. Good luck, hope you find the car you want.