I have a 2002 640LC4-E - it's been used for a couple of trips, the longest of which was across the Sahara and through west Africa. For this it had a 640 Adventure tank fitted and other mods.
As regards mods/accessories the bike's current setup is:
KTM rally footpegs
SW Motech sidestand
KTM/Akrapovic slip-on silencer
KTM dual curve ignition box
Stronger clutch springs
KTM luggage rack (the small one that comes as standard on the Adventure)
KTM comfort seat
KTM 18 litre tank
Touratech GPS mount
Touratech handlebar cross-brace (to mount the GPS mount)
Touratech IMO rally computer
Touratech roadbook holder
Touratech rally bracket (to mount the IMO and roadbook holder)
KTM neoprene fork gators
The bike came as stock with an engine guard, mainstand and handguards.
For luggage I use an ortlieb rucksack strapped to the rear rack and a KTM tank bag.
Apart from the clutch springs, the only mod I've done to the motor is to upgrade the mainshaft bearing with the part from the 03 on models. There's loads on this topic on this forum - check the thread index.
IMHO with handguards, an engine guard, some means of mounting luggage, the 18 litre tank and the comfort seat, the LC4-E makes a decent adventure machine. Next for mine is a set of supermoto wheels - just about 2 bikes in one.