Sounds like you should flog it - you can always buy another if you realise you've made a mistake.
I think the z takes a bit of time to get to know and get the best out of. Mines a bit clunky around town and tramlines like mad. The suspensions very firm and on poor roads its a bit of a pain. I also can feel slow on take off and I think thats because its quite heavy and unless you're caning it you may be only using 2k rpm - and if the gearbox is cold I'm shifting from 1st to 3rd because I cant get 2nd. Diesel hatches are coming past me, but thats only because they're being thrashed! I just cant be bothered on the commute.
Thing is, when you're in the mood, once its warmed up and you've got a decent road under you and you're driving at a decent pace, everything starts to make sense. The engine is fab when its revved out and so smooth and flexible, the ride is good and it goes round corners beautifully, the smallest gap in traffic becomes an overtaking opportunity... I could go on. Oh yes and its very lovely to look at - I cant think of many better looking cars.
Its got real character and thats rare these days - its really got under my skin and I love it!!! (still dont really enjoy the commute in it but I've got my vw shed for that, which is like driving a compact cosy sitting room around - and its got a cd that works)
Sell it and let someone else love your Z - it deserves it!