I agree with you, as soon as someone mentions "Wimbledon" on TV I might as well forget selling anything much until the kids go back to school. Rather than listing loads during quiet periods I've found it fits my life-style (and boredom threshold) better to list one new item every Sunday morning.
At 50 new items a year (back then I was lucky to get 4 - 5 sales a year) it didn't take long to reach 200 items listed. That seemed to be a magic number for me and I've never reached 300.
I think listing that way has helped me on GS. I don't know how it selects which of my items it shows (I think "Date Listed" must be a factor) and having something listed almost every week gives me a wide spread of dates for them to choose from, so I can always find a few of my items.
Congrats on your sales, perhaps a sign that the draught is beginning to end?