I would say let the business' do the talking. I would be happy to let business' reply to the forum, obviously for free... In giving this free information they will be raising there profile and maybe there client base.
To me it's better than a static list, the more a business gets involved the more chance they have of gaining some work.
I'm not saying that I disagree entirely with this, but it has two problems. PN is essentially advert free (no dodgy Flash based graphics or Google ads or signature images etc) and it is difficult for businesses to just answer questions without essentially promoting themselves all the time. What you might end up with is an answer to all the plumbing questions but with them just essentially being "You need a plumber for that" followed by their details. There are a couple of notable exceptions to this on PN thankfully. The Directory contained all that - many of those advertising in the directory signed up to do that and never posted anything in the forums and that was fine. It is very hard for people not to recommend themselves all the time in the forums and not allowing self-recommendation was less work than fighting the determined self-promoter. Although perhaps in the end this just meant less activity.
My second problem is that you're judging the persons ability to social network, not their ability to fix your sink (or whatever) and many good people will be out working rather than answering every question about how to connect English taps to old French pipework. If you have a house here, you are likely to want to learn about local services and which are good or bad.
In addition, Pont Noir isn't a "go to place" for these sort of questions. It's mostly about the Creuse. The Directory was entirely related to that since you had to be registered in the Creuse to have an entry. Nothing wrong with asking about plumbing questions on Pont Noir, but other forums will have more expert advice because they have plumbers from all over France, for example.