I don't think sodium *elimination* is wise, but definitely making sure that you're not overloading (which is hard in our typical western diet). I know some other women here will weigh in with more info but here are my thoughts on sodium/pre-e (not based in anything but conjecture).
I think that in the Western diet we typically eat EXTREMELY sodium rich foods- fast food, packaged foods, sodas, many people salt their already salty foods... it's an overload to the extreme. If your diet consists mainly of home-cooked foods, fresh fruits and vegetables, little/no boxed/canned foods and you aren't salting to high heaven, you are probably okay. We NEED sodium in our bodies, so eliminating it might only exacerbate a problem rather than solve it. We just don't need the hundred million pounds of it we eat in a single meal. There has to be balance, you have to give your body what it requires to function.
Spend some time reading the boards and ask lots of questions! Get a blood pressure cuff and monitor at home. You can download my [url="http://www.dynamicdoula.com/BP.xls"]chart[/url] (my data is in there but just remove it and put in your own) to keep track over time, and then take that to your doctor when you see him/her. Also, start thinking about finding a doc who is more aggressive about looking after your wife. Pre-e is not something you want to 'wait and see how things go', it's something that you want to be on top of the whole time. One of the hardest things I have found there is to do is to simply trust your instincts, and call/go in if you feel something is wrong. Support your wife by encouraging her to trust her gut; if she thinks something doesn't feel right, back her up and take her in. It sometimes is just a 'feeling' you get. The hope is that it turns out to be nothing at all and you go home with reassurance. :)
I'll see if my husband would be willing to pop in here and offer you some of his own perspective; this is our 3rd pregnancy with hypertension/pre-eclampsia and the first time we've actually had some decent management. He has his own worries for sure, he was terrified I would die last time but things are going much smoother this time around. It might be helpful to have another guy's perspective?
Keep talking and asking questions, the women here are amazingly knowledgeable (moreso than many docs, in my experience) and will offer as much support as you can handle receiving. :)