If you are mechanically deficient and don't plan on getting at least to Home Hacker level of mechanics (ie. me!

) then forget it! Mini will cost you TOO much to repair/maintain and upgrade if you have to take it to the shop for everything other than to top up on fuel and the occasional wash'n'wax... A shop will charge you $70 per hour for even the dumbest of jobs.
Buy a honda jazz or one of those really tiny Diahatsu's (that look alot like a modern mini if you ask me... more so than the Bini does, esp in the size department)
[EDIT] Sirion that's it... don't you guys think it looks like a Mini??? just a little bit?
Even a Swift conversion into a mini will mean BIG BUCKS and usually are attempted by people who know at least alittle about what they are talking about to be able to do some or most of it themselves to save money...
My advice, stop going on third party advice (ie. My mate told me this, they say that...) Go ride in a Webber 45 1275 A series car, then go ride in an SPI, then check out some cars in your price range and work out if the mini is for you.
If it's reliability you want, then a Corolla sounds like it fits your bill more than anything else. The other thing is, an A series SPI conversion of some sort or Jap engine conversion is totally a custom job and as with all custom jobs, how reliable can that be?? certainly not 100% surely... Just keep in mind that an average mini's age is around 30 yrs old, so it will be a case of 30yr old parts in the car which kind of defeats the reliablity issue.
That said, if you want to learn how to fix cars and get dirty then the Mini is the ultimate car for that!