It's no secret that I love cookbooks, but I am hesitant to give them to people as gifts. Will they think I hate their cooking? Will the gift be perceived as a hint that they need some help in the kitchen? In the end this a very situation dependent question. I have given two cookbooks as gifts in my life. One was for my sister-in-law who had been ogling my Kosher By Design. So I surprised her with one of their own. The other was a kosher cookbook for a friend who was just starting to keep kosher and was a little confused about what she could and could not cook.
Men, this is an even tougher situation for you. Can you give your wife a cookbook? The short answer is yes and no. If she's been eyeing a book, dropping hints about it etc. then sure go for it. My husband got me a great set of books about cake decorating for my brithday. However a cookbook out of the blue, especially beginner type cookbooks make many women feel a little insulted. I'll never forget the lady who came to shul and complained that her son had given her a cookbook. I thought "wow, what a nice kid. Randomly bringing mom gifts". She interpreted this as his complaint that she needs more variety with her kitchen and moaned "I'm 62. I can't keep up with these lakewood wives".
An alternative is to get a nice kitchen gadget that will cut down on time in the ktchen or has a cute function. You please the cook/baker and are actually saying you want them to cook more.
On the other hand, if the cooking really is sub-par then maybe this is the gentlest way to suggest some improvement is needed.
Al gift giving is really about knowing the recipient. If you don't, then you're going to fail at whatever gift you select.