I was reading a post from a gentleman in the FLR group on FetLife and the issue he was dealing with was that it was hard for him to imagine spankings from his wife as either being punishment or motivation since he craved and enjoyed them so much.
Certainly, we all enjoy and crave those spankings from our loving wives that remind us of their love. Feeling my hard cock against her smooth thigh while she lights my ass on fire is certainly provides a wealth of sensations I could always use and enjoy more of, and of course a Valentines day sentiment befitting the day.
Following is my response as I believe there are always things that can make a spanking less desirable. I think every couple needs a certain kind of spanking available in their repertoire that won't be craved, desired or enjoyed.
For me, I think there might be a lot of motivation available in implements and/or techniques.
If you have a small assortment of implements and can't make the investment, then repetition could be a method available to her. Perhaps what would be a normal intense spanking but instead of it being over... you now are sent to the corner for a specific time letting you reflect on the event and giving her time to re-energize and then 2nd inning, corner time and third inning etc..
For a good assortment of some seriously effective, yet inexpensive wood paddles I would suggest Woodrage Paddles. http://www.woodrage.com/ Their 3/4" oak 16" paddle with 3/4" inch holes should certainly be feared when used on the sharp edge side. (holes are smooth chamfered on one side and sharp on the other... The Bastards).
They also have a 3/4" Oak Hairbrush paddle that I can attest deserves a mountain of respect.
There are many fine makers of implements but these are two that I can personally vouch for that offer products of quite decent quality, at very reasonable prices.
Of course there are other scenarios too, one that appeals to my nature is being in the corner watching a nice big bar of ivory soap soaking in a bowl of warm water. When it's time for your spanking a washcloth and the softened soap can be used to clean out your naughty mouth, and still provide something tasty for you to bite down on while being paddled.
Naturally, after your ass gets good and tender if your wife should so choose, the bowl-full of soapy water can very easily be sucked out with an enema bulb and installed into your well lubed ass. Then, a dozen or so good hard paddle smacks will insure the solution is effectively and deeply installed, giving you more to think about while the remaining bulb-fulls are lovingly prepared, inserted and paddled into place.
If humiliation is part of your normal activities, you can optionally be dressed just in time to be stood in the bathtub where you can soil yourself and ordered to clean up your own mess.
The possibilities are truly endless.
Hope this helps...