Generally it seems the earlier you go in regards to Fabias, often the better the rust proofing is. As towards the end of production the bean counters got in and started reducing factory rustproofing etc. I've seen more Polos with hammerite and holes than Fabias, but it's not impossible. Although that's true for any car as there's a bloody myriad of factors that contribute to how and why a car rusts, where it rusts etc.
That being said, I've got a 2006 Mk1 with 74k miles that's now doing 12k a year in all conditions... in Scotland. Got some surface rust on the sill ends at the rear, and a bit in the rear arch tubs, I'm going to sort that out in the summer so that it at least delays the inevitable with any luck. @DoctorBoostaLot has a thread going now documenting the welding he's doing to his Mk1 Fabia, if you can do work like that, or find someone reputable to do welding work (thin on the ground getting, but still possible) then you'd be doing pretty well, I reckon.
So aye, a good Mk1 still has life in it, and just tidy up any rust that appears as and when it happens. If you've got a clean base for a car, then that's fine. It's easier to replace an engine than most metalwork, keep that in mind.