I have a 99 Corolla, the gen before the current car. It was only used for a year before i bought it in 2000 and i have owned it ever since. I've put 65,000 on the car since then and over the course of the past 5 1/2 years I have only spent about $1000 total on maintenance and 'repairs' (excluding the new set of tires/wheels i upgraded to). I really haven't done anything special to the car over my course of ownership, the wheels and a K&N air filter are about it, and the thing just keeps on ticking. I also put Mobil 1 motor oil in it so i only have to change the oil about every 10,000 miles. Though I've never been a big fan of the current Corolla (de-evolved from an independent rear suspension to a solid rear axle!?, too tall, stubby nosed) it's a much better choice than an Ion. My sister just bought a 2005 Ion earlier this year and has had a few problems with it already. Plus the ergonomics of the Ion are all jacked up, the torture chair rear bench seat, center gauge cluster, mismatched design shapes throughout the interior. They rectified some of the problems that plagued you 2004 for 05, engine noise is reduced through the use of QuietSteel behind the dash, but overall I'm not impressed by the car.
You will also enjoy better gas mileage in the Corolla. I believe the Ion gets an EPA rated 34mpg on the highway, the Corolla get around 40-40+ depending on your driving. If you're not in an over all hurry there will be a new Corolla appearing either fall 06 or spring 07, i might wait till then if i were you. But if your looking to unload your plasticmobile before then, i would suggest depending on your needs; a Corolla(an XRS if you want to spend that much, when the cheaper tC is quicker), Scion tC, or a Mazda 3. Plus there is also a new Honda Civic out their now which, though seemingly quirky (2 gauge pods?), gets good gas mileage and comes in a variety of flavors (sedan, coupe, hybrid, SI).
Also, the Corolla XRS may hav 171hp(lost 9hp due to the new SAE hp ratings) versus the Scion tC's 160hp, but look at the torque #'s XRS-about 128lb/ft, tC-about 160lb/ft. The XRS's Celica-sourced 1.8L VVTL-i is a little gutless below the 6000rpm mark, while the tC has the 2.4L VVT-i four from the Camry which keeps you in the seet spot better, due to the engine's larger size.