Sorry, Rolf, but I think that's bad advice. My last Z4 did not have NAV/iDrive, and I was sure not to make the same mistake with my new ride, and I am glad I didn't. I haven't heard of floods of people having problems with their iDrive- a couple of folks here and there, but it's not really a component which you would expect to have serious problems, as it's primarily software driven, anyway.
The NAV and iDrive are really must haves (Mainly the iDrive, which you can only get with the NAV option- that's why it seems expensive). While you can do SOME things without them, it is nowhere near as easy and full featured as with the iDrive. Not only do you get the added functionality of the iDrive, you also get 12 GB of hard drive space to load up your own music collection (which reminds me, get the iPod integration- though that should come with the premium sound, which is also a must, as stated above).
I'm assuming you'll have the BMW assist, but I'm not sure if you get that north of the border. If so, you can actually send info from Google maps right to your iDrive, where you can load the address to the NAV, or call the place with your bluetooth phone. That's pretty cool, and I have to admit I have already used that feature a lot more than I would have expected.
(And if you don't get BMW assist up there, don't worry. How bad can it be? I mean, you get to live in CANADA, after all...)
While I have not been a huge fan of BMW's Nav system in the past- I've used tom toms, magellan, and garmin products - this new iteration is far superior to anything they've put out recently, and IMHO superior to the Garmin unit my wife is using. You also don't have a power cord hanging in your face and messing with the beautifully designed interior.
Unless you are only planning on dropping the top and enjoying the sound of your new car as you tool through roads of Ontario (that is, if you make calls, listen to music, or take a road trip or two), you'll be wanting that iDrive. Trust me.
As far as the other stuff, I have the PDC and, while it certainly has a great "wow" factor for your passengers, I haven't really found it as useful as I thought I would (of course, I've only had my car for a month, and haven't done a ton of parallel parking). The wind deflector you can always add later- I didn't get it initially, but am thinking I may bite the bullet soon on that. At least it's easy to yank off and store when you don't need it.
I would really reiterate what was already stated above, though. This is an expensive car, an indulgence. Right? Load it up. Don't go nickel and diming yourself (hope that reference carries north of the border, as well) over options you'll regret not having later. It will help the resale down the road, and add to your enjoyment in the short run. If you're looking at a 35i, along with DCT and M suspension, note that the 35is comes with those standard- which makes the price difference between the two not as bad (at least down here). Just something else to consider...
Good luck!