Thanks very much to rose hip and TheKittyKat for your replies. They're most insightful and helpful, and I really appreciate them!
I don't wish to take this thread too far off-topic, but I'd like to reply to the points that you both raise.
rose hip wrote:
No idea if this is what your wife is after CH, but what if you just responded with a similarly cheeky "Oh, you need to be punished, do you?" and then pleasured her until she couldn't take any more?
Oooh... I'd like to try that! 
rose hip wrote:
It sounds like she's giving you an opportunity to take control, but you're not sure what to do with it.
Yes. I'm faltering somewhat, for reasons that I'll explain further below.
TheKittyKat wrote:
Whislt communication is VERY important, I would nevertheless caution against taking conversation as the only measure of what your wife might want. My OH and I can both sometimes be a bit reticent about talking about something which we enjoy but feel we shouldn't (due to social stigma, personal backgrounds or whatever). Nevertheless, when we're in the bedroom, it's a different matter, as we feel we can relax and enjoy whatever in the heat of the moment. In other words, could this be one of those situations where it's something that she secretly would enjoy, but doesn't quite feel comfortable enough talking about in the light of day?
I think you've hit the nail on the head there. Whilst my wife and I generally communicate very well and openly, we both tend to clam up when it comes to being sexually adventurous.
In my wife's case, I think it's because she still regards herself as a "nice girl" and wants me to take the initiative -- and perhaps the "blame" -- for anything that's beyond the vanilla.
In my case, I feel conflicted and guilty about my desires to be a bit "nasty" in the bedroom (albeit in a playful and loving way) because I'm used to being a "nice guy". When I do mention these ideas to my wife, I tend to do it in a tentative way. If she seems half-hearted or less about them, then I back down quickly and berate myself for making such a suggestion. It's a shame, because I think many of the ideas that I'm binning (either not mentioning or backing down on) are imaginative and potentially a lot of fun!
So, I think you're right that conventional communication (i.e. prior conversation outside the bedroom) might not be the best approach in this case. Perhaps we could create a "bedroom zone" in which we can leave our "nice girl" / "nice guy" personas behind and feel free to discuss / try anything we fancy, unless one of us uses a "veto card" or a "safe word". Hopefully that would enable me to leave my guilty feelings behind and express myself freely.
If anyone has any ideas on this, then I'd be very grateful to hear them.