Like our friend Bach, I too always keep a body of Marsala wine at hand for both drinking and cooking, especially in preparing a great many Italian and what I think of as nouveau-Japanese dishes. With that exception though, I have only rarely purchased wines entirely for cooking as there are (whether one is a critic or not) invariably enough left-over wines that can be used for that purpose.
Being a believer in the fact that few wines should be held responsible for their condition on the following day for drinking but that many will hold their charms for cooking for a week or more if well stored, my tradition has been to transfer left overs to small plastic bottles that held mineral water, to reseal them and to refrigerate. With sauces I do not hesitate to "blend" some leftovers (e.g. Cabernet, Merlot, Petite Sirah based wines) in the same plastic bottle (call that my saucier's solera system if you like); but very distinctive wines such as Barolo, Brunello or Chateauneuf remain each in its own plastic bottle. Same with whites and with sweet wines. The moment that the wines start to go off, they are tossed, bottle and all, into the trash basket.
If I were to purchase wines entirely for cooking (and keeping in mind your need for kashrut), those would probably be from high quality/good value producers such as Tabor, Galil Mountain and some of the Herzog wines. If not concerned with kashrut the wines I would purchase largely for cooking would probably include those as well as Beaujolais Villages, Chianti and many of the wines of Pays d'Oc.