Yes, it's worth buying. It's not without flaws, but overall the depth and width of the gameplay make it very worth while. It's a game you can make what you want of it, unless you want to smash cars up.
GT3 and GT4 are basically all I've played since I bought my PS2 3+ years ago, aside from doing some of the driving bits for my wife in the Jak series.
We have a whole forum about steering wheels and cockpits. Check it out.