The 3.0 diesel engine in the X5 is a pretty robust unit and the 2005 version does not have a diesel particulate filter, so you don’t have to worry about this clogging up.
Some additives are beneficial when used in certain conditions, although it is often difficult to separate the placebo effect from any factual evidence. Given that you use Shell V-power, which has additives in the mix, I would not put any further additives in at this stage. As you say, the oil is changed regularly and the vehicle is running well.
Although you only cover 5000 miles a year, you do no mention the length of each journey. If you take a lot of short journeys, as opposed to a few long journeys, I would possibly consider taking the vehicle for a longer run periodically to help keep any build-up of soot at bay. I have a 2005 BMW E53 X5 Sport 3.0 diesel auto. I bought the car from a BMW dealer with a full BMW service history and 29,875 miles in May 2015. I drive around 5000 miles a year and always use Shell diesel and sometimes Shell V-power diesel.
Some friends have commented that there might be a build-up of soot due to my low mileage. I know that BMW do not usually recommend additives, but have found out that they now offer diesel additives. Do you think that putting a bottle of this in my X5 would be beneficial? At the moment, the car is running perfectly and the oil is changed once a year in between services. Paul Finnegan