Hi, I bought a 2005 xtype estate 2.2d last year with 70000 on the clock and 12 mth MOT but it had a full Jaguar service history so I was reasonably confident until I took it to my local Jag dealer for a full service. :( They highlighted several things mainly the fact that the brakes needed new discs and pads all round, various oil leaks etc etc, the upshot was they wanted to charge me a cool 2500 to get the car up to their standards. My local Indy checked out the brakes bearing in mind the 12 mth MOT reckoning I should get at least another year or so out of them, the oil leaks were miniscule bearing in mind they are oil burners anyway. Basically he said Jaguar want to bring an old car up to their standard as it left the factory if people are prepared to pay for that fair play.
I am very happy with my car it goes like a rocket and puts a smile on my face when I drive it.
With regards to a Terraclean, the cost certainly is a factor but I would do my research, go on other Forums as well as this one of course, a lot of people make do with cleaning the EGR and blanking plates etc.
Good luck.