I've owned a 52-reg 1.9 dCi RX4 since 2006, and it's now coming up to 90,000 miles. Touch wood, it hasn't had the major problems that some people have experienced, and I've generally been pleased with the basic Scenic virtues (space, lots of storage, reasonable comfort) allied to the 4WD ability for ice/snow/mud.
valve and a glow plug (which could happen on any car). Rear brake pads need to be watched for wear, and/or seized calipers. Has drivetrain vibration for last 20,000-odd miles, I guess, due to worn mountings for the damper rings on propshaft, as others have mentioned (you get used to it but try gently placing your finger on the rear view mirror while driving along - amazing how much more stable and sharp the image becomes when you counteract the vibration!). Keep an eye for
leaks from the rear diff and if so, check the
level regularly. I had the same exhaust breakage problem as rxphoar but the downpipe and rear section are still the originals. Oh, and the radio reception has always been poor!
I know others have been less lucky with the oily bits but overall I can't say I regret buying the car. Thing is, the age and condition of many of them now means you would be wise to look very carefully at the one you want, and even then, a nasty surprise might crop up.
It sounds as if you might be considering an RX4 as a second or third car, and if so, and you can get one for a good price and after checking it over, you could do a lot worse for a roomy 4x4 - just don't tie a lot of money up in it. I'm afraid I do a lot of urban driving these days (so low 30s mpg at best) but on a long run, I'd look to get around 40mpg or a bit better, though that is with an engine tuning box and I drive more to exploit the additional torque than to blast along at higher speed! Tyres (Michelin Synchrone then Goodyear Wrangler) have done 20,000+ miles easily.