DAB will always be an efficient use of the electromagnetic spectrum to use broadcast for things that are actually broadcast, because if you have a mass listenership, then best to use a one-to-many channel, not a peer-to-peer network.
DAB's problem is that it falls between two many posts. There is choice over FM/AM, but now mainly of BBC stations, plus Planet Rock.
The sound quality isn't better. Mobile reception is worse. Coverage is worse. The choice of sets is very limited still - the only mobile phone with DAB was the Virgin Mobile Lobster, now dead.
Freeview and satellite provide a much better listening experience for all radio channels over DAB. RDS still trumps DAB for auto tuning and the "traffic programme" service.
And, as the BBC launched DAB before MPEG2 was ratified, there is no easy path to DAB+.
And there is no "digital radio switchover" date to focus minds of both broadcasters and consumers.
In the end DAB is a technology looking for a solution, not the answer to consumers prayers.
If you were to ask people what they wanted from digital radio, I am sure they would want:
1) Universal coverage better than FM and AM combined (as it is to replace both);
2) More choice of stations and formats in both local and national configurations;