Its 10 years old but was 5 yrs before its time and as stated will never match modern games for pure eyecandy, but you dont play gp4 for that, saying that it can be made to look pretty damn good! If nothing else the AI are as good if not better than the AI in any modern driving game.
After a few of hours messing and getting used to the file system its easy to mod and get upto 2010\11 the cars are all there the tracks also team graphics menu data everthing is updatable, hell of a lot of rough to go thru to find the diamonds but they are around and make it look very good. look for zastools to install .cuh (cars and driver graphics packs) and .tup (track packs) files.
Also a big download but has all the 2010 tracks and cars is the vazalm 2010 mod its a bit too busy for me but you *could* take it apart and just use the stuff u need.
shitloads to make a good game better!
lot of cars tracks and mods mostly old tho last season mod is 2008 i think!
look here for controller setup, im sure it`ll give you split axis which a lot of ppl struggle with in gp4
as already mentioned
id been away from this game for years but spent way too much time trawling this site recently, pretty much got everything you will need to get a good experience with gp4.
get gpxpatch here, it is a must, very easy to add some very nice screen overlays, load tracksets, edited perf files and lots more.
edit added a couple of links