Thanks for the many replies. Cars seem to be one of those things that excite vastly different opinions and experiences. I appreciate all the feedback and insight.
One more factor that I've been trying to keep in mind is the overall size of the vehicle. My wife is not a confident driver and doesn't enjoy driving. She's reluctant with anything larger than what we've got (which is what she learned to drive in). That's another reason why I've shied away from the SUV-style vehicles. There is a tradeoff of course - wagons are inherently bigger than their sedan equivalents, but some vehicles seem to have a TARDIS-like quality which gives them better space inside without being substantially bigger on the outside. I took a Nissan Qashqai for a drive last year (just for kicks) and was bewildered at how it seemed to ride so high and loom large on the road, but getting in an out of the car didn't feel any bigger than my Altezza. Weird but true.
After reading all the replies thus far (and keep them coming, it's all useful to read), I'm teetering back towards the Subaru. It sounds like the cost/reliability issue is a variable one. I'm not one to shirk servicing, which sounds like it might mitigate many problems, though there's always a risk of picking up a lemon. The one that I drove that I liked most has 130,000 kms on the clock, which is about 50,000 kms higher than my Altezza when I bought it in '06. but my distance travelled these days is a lot lower. I average about 5-6,000kms a year, which means I would be owning the car for about 10-12 years before I hit 200,000kms overall. If the mileage-based maintenance required over that time is minimal, then it's a viable option. However, if the vehicle starts to fall apart (despite regular servicing) at 150,000kms then it's a different story. I'm planning on contacting a local Subaru specialist workshop to get an idea of actual servicing and maintenance costs for the model/year/mileage, which may assuage my concerns somewhat (or reinforce my fears).
The comments about Avensis are interesting. It's one of the cars I'm hoping to look at this weekend. It's hard to picture an unreliable Toyota, but I guess every maker has their lemons. I had an '84 Celica that seemed to be a frankenstein model and it was ludicrously expensive to maintain and repair (compared to my current Altezza). The other car I've got in my sights is the Mazda Atenza/6 wagon. There seem to be a few of those around, which gives me a bit of choice. After trying those models out it might clear my thinking somewhat.
Personally, if I were going to buy a Subaru, I'd get the older model that's been fully rebuilt. You can find a bunch of them on TradeMe with the engines having all the important stuff done to them, gaskets, belts...etc, or even a full refurb of the engine. I'm sure you can find later models with the same stuff done.
In general when I buy a car, my search criteria are usually: "rebuilt", "reconditioned", "receipts". My partners brother found a Ford 4x4 that had been fully reconditioned (engine and gearbox) by the mechanic that owned it. Got it for 5 or 6k, but he knows it will go forever.
Otherwise, consider the Corolla wagons. Sure, you don't get the creature comforts of the Subaru or BMW especially, but at least you'll know for sure it will get you where you want to go!