Matt,
It all comes down to what you intend to do with the vehicle, and what condition you bought it in. For example if you were running one every day, then you would need to spend longer with the grease gun and doing oil changes/running gear inspection. If you only plan to use it every so often, it's not too bad. Obviously the more you run something, the more problems you'll have, and the more money it will cost.
For example when I restored my Sabre I fitted a new set of track, sprockets and wheels. Every now and then I will randomly check a few wheel/track nuts for tightness and give it the once over to check for pads with problems etc. I know everything is in good condition as it's only done 100 or so miles since it was all fitted, and I know I fitted it. If I bought a vehicle from someone else, I would be a bit more cautious. The last thing you want is something flying off at high speed.
I spend more money on bits I don't need than on bits I do need. For example I have spare engines, wheels, filters, anything which can go wrong or wear out. I also read lots of comments from people who say tracked vehicles require loads of maintenance etc. Maybe I am missing something, but I don't think you'll spend any more time working on say a CVR(T) than any other armoured or large vehicle. A 432 is bigger and heavier, so maybe it'll take you a bit longer, but it's certainly a lot less work than keeping something like a Stalwart on the roads.
Major expenses are powerpacks/engines and track. Wheels aren't that expensive, but you need lots of them as they can and will fail at any time. FV432s seem to have problems with the rear idlers breaking off, I've not seen this myself but the guy who bought my 432s has had it happen. Obviously something to check if you're going to buy one.
The bottom line is, buy the manuals, read them, and do what it says as often as it says, and you should be ok!
Chris