VHF FM broadcast transmitters will eventually be closed down. (Under the original plan it should already have happened but, just as the digital TV switchover ran more than 10 years beyond its planned date, the switchover to DAB radio is also running well behind schedule). So, if you're planning on keeping the car for more than a few years, DAB definitely makes sense. (Of course it also gives you a wider choice of stations, such as the excellent BBC Radio 4 Extra).
However if you're planning to use it abroad, you need to be aware that there are two technical standards for digital audio. The UK and Norway were the first to embrace digital technology and adopted 'DAB'. The rest of Europe delayed the introduction of digital radio and adopted the improved 'DAB+' system. (Norway is now gradually switching over to 'DAB+' as well. The UK is likely to follow suit eventually). So any radio that you want to receive digital signals both in the UK and abroad mustbe compatible with both 'DAB' and 'DAB+'. (Many receivers now are but it's possible that some might not be. So check the specifications!)