I'm not as much into mine when it's cold vs. when it's warm, either. Several reasons for this...
I think I love wearing them when it's warm because you don't have to wear anything over them and you're still warm. This is true for inside and (if I'm brave and have the opportunity) outside. I really love wearing just my diapers, plastic pants and a t-shirt and when it's warm, I'm just more comfortable (temperature wise) doing this.
Also, most all of my adventures going out in my diapers are when it's warm or hot outside. I may be crazy but for some reason, I feel like in the summer I can wear diapers under my shorts and let them be more obvious and if anybody says anything, say, "Well I usually wear more over them but it's really hot out today!" This is true whether it be some stranger seeing me in the grocery store, or a neighbor seeing me walking up to the mailbox. And I guess that over the years, I've just grown to associate my diaper fun more with summer than the rest of the year.
But perhaps the main reason is, my diaper fetish is rooted in very early memories that are all associated with summertime. After being born I was sick for months and had to stay in the hospital. When I finally came home, it was springtime. So my earliest memories of being happily at home were when it was warm outside and I was wearing diapers.
Most of my early memories of seeing other kids having wetting accidents occurred on sunny summer days. Also I associate sunny summer days with riding around the neighborhood on my bike when I was a kid and seeing clotheslines full of diapers hanging outside to dry. Because of this, you always knew who in your neighborhood still wore diapers.
Then, over the course of the rest of my life so far, it just seems like 90% of my most cherished diaper memories are all of things I did when it was warm outside (that time I walked all the way around the block at 2:00 AM wearing nothing but bulky wet cloth diapers with a pacifier on a ribbon around my neck comes to mind).
All this being said, I do still enjoy wearing them in the winter when I'm overcome by the urge. And I've gone out in the winter wearing them under my clothes. But for some reason I do prefer warm weather for this. And it seems like every year, as soon as spring arrives, I start thinking "It's Diaper Time again!" and am about driven crazy by being "diaper horny."