You wont find better in this price bracket IMO, no point trying, at least until the 370Z is out, which is most likely my next car
Keep it and get it modded, just have some fun with it! If you work out how much you'll really save my changing car, it never works out to be much. Remember that the Zed is pretty frugal for what it is and if not driven hard gives good MPG. Plus all fun cars, bar the lightweight sports cars, will be walloped with tax. How many MPG do you get from the ZR out of interest?
Also get some new insurance! Thats mental prices. We have the Zed and missus corsa on a multicar policy which is £800 for both of us on both cars and me with 20k mile business use!