My guess is your going to get about 50% for and against, with SEVERAL people screaming you must replace or the big bad radiator will come get you and your kids at night while you sleep if you let your car go over the 100k mark without changing.
Personally, the vast majority of failures I've read about with E46's were with the expansion tank and radiator itself failures were more in line with typical car failures and not an issue, unlike the E36's which cracked at the top and failed prematurely. I'm no expert, but when I had the Indy shop working on my car after I bought it and had no service history, I had them do the water pump, thermostat and replace any hoses that were bad and they felt the radiator was solid and should simply be flushed. All this was done per their recommendations seeing 5-6 BMW's a week in their shop. The only thing I wish I'd had them do was the expansion tank, but I'll wait until I get a few more things done and just keep a close eye on it until I decide to either have them redo the coolant and replace the tank or I'll do it this summer.
Ymmv, but this is not just an XI specific thing so search on here in the general area to make your own mind up.
Last edited by miweber929; 01-03-2013 at 07:52 AM.