I owned a Prius for three years, so can give you a view as to it's strengths and weaknesses.
For my 40 mile each way commute to work, on slow A and B roads (average speed around 40mph) the Prius gave excellent economy, about 62mpg in the Summer, dropping to about 56mpg in the Winter (it is very temperature sensitive, more so than many cars). I reckon that the Prius saved me around Ã‚Â£1500 a year for my 20,000+ annual mileage (compared to the Mercedes SLK I had before
I changed jobs about a year ago and my commute dropped to just a couple of miles, with the odd long trip of 100 miles or so every couple of weeks, plus average journeys of about 5 to 10 miles at weekends. The Prius fuel consumption plummeted to around 45 mpg at best, I don't think I once managed to get more than 50mpg from it doing these short runs.
In my case I also kept an old Daihatsu as a tow car (the Prius cannot legally be fitted with a tow bar in the UK, despite what some will say). I sold the Prius a few months ago and bought a Honda CRV diesel. This is nearly as economical as the Prius (it returns about 42mpg), but has allowed me to get rid of the Diahatsu, as the CRV will tow pretty well.
My advice would be not to get a hybrid solely for fuel economy if you only do short runs, as it won't really pay for itself at all. At the moment, a small diesel will almost certainly be cheaper to run than a hybrid of any flavour for short runs and will also be cheaper to buy. My wife has a Citroen C3 diesel that returns a steady 60 to 64 mpg when doing a commute to work of 5 to 6 miles each way, which is far better than either the Prius or Civic will manage for that sort of journey.
There are many other extremely good reasons for getting a hybrid though, including the fantastic driving experience that the Prius gives. With no gears (the Prius is not an automatic at all, it simply has no gearbox or clutch in any form, just a clever power split device and a directly coupled electric motor) and continuous drive from a standstill to over 100mph, lots of torque from the electric motor and cheap road tax, it has a lot going for it.
The Civic is a much less capable hybrid, in my view. I test drove both before opting for the Prius and it was no contest. The Prius is by far the better technological solution, as well as being more economical in practice and a much nicer car to drive.
With regard to the NHW10 import, I would advise you to think very long and hard before going down this route. The main screen will be in Japanese, with no English translation available, the radio will only work with a bodge converter that shifts the frequencies to the UK spec, RDS won't work on the radio, spares are, to all intents and purposes unobtainable in the UK, as the car was only ever manufactured for the Japanese domestic market, and lastly NHW 10 batteries will now be pretty much at the end of their life as the car will be around 9 or 10 years old. NHW10 batteries can possibly be rebuilt with NHW11 modules, but it wouldn't be a cheap job if you needed to pay someone to do it. Finally, the NHW 10 performance was pretty dismal. The NHW 10 was really a marketing and development experiment by Toyota, who never intended the car to leave the shores of Japan. Finally, you will pay full whack road tax on the NHW 10, as it doesn't qualify as an "Alternative Fuel Vehicle" to fit in the cheap tax bracket.