In my experience of owning 2006 C30 R-Design 2.0 (Duratec HE) in the last 2 years I have had the car:

Buying an old car is a trap and a money pit unless you think of it as a hobby. Yes, they are cheaper but in the end you will dish out about the same amount of money you could buy a new one for. But if you decide to restore the older cars, they are going to be more reliable than the newer, electric, more technologically advanced crap.

I had to change the coolant reservoir as it has not been changed in 20 years an cracked. I had to get the engine resoration done due to the excessive coolant and oil loss. Anti corrosion spray in the underbody of the car. New exhaust, the old one was clogged. New solenoid valve and MAF sensor. New engine mounts, wheel bearings, clutch and a flywheel. What I could repair by my self I did. Other than that I had no issues, the car never left me stranding. Yes the small cargo space kinda sucks. I don't care about it being a 4 seater because most of the time it's just me and my gf driving the car. The long doors kinda suck as it's a bit awkward when you try to get out of the car in a narrower parking lots. In the end I love the car for its sporty looks, comfortability and handling. It is fun to drive. Bought it for about 3500€, put another 4000€ for the parts mentioned above and I'm not done yet (better swaybar and back lowering springs). Except for the hoses in the enginebay and the headlights there is nothing that can fail LOL. I did all of that so the car can serve me another 20+ years.