Martin,re your quote " when will the next big bill be", I've just been in that self same situation.My 94 Range Rover needed a small brake job, which turned into three weeks and almost £1000! By the time I was told about the cost, a lot of the work had been done, so had I decided to scrap the car, I would still have had a hefty bill, and no car. And of course I would still have to find (and fund) a replacement.
Well, I had the work done, and tried to smile as I paid the bill, which was probably half the car's value.But, in hindsight, I don't regret doing it, because I still have a car I know and love, which has carried me all over the UK and Europe over the last few years, and which I would find difficult to replace. (its a LSE Range Rover, with lots of special equipment).
So I now accept that the actual value of the car is secondary; the main qualification is that it suits my purpose. This is the first major cost in over 30,000 miles, and I've no doubt it won't be the last, but I've still got the car I know and trust.
(plus the fact that Herself says she just cannot image me ever driving any thing else!)