Some of the talent that appeared at Wrestlerock was piggybacked over from the Crockett Cup so that had to have been a factor. The AWA roster was pretty thin at that point, at least when considering running a Supercard.
It's true about the AWA numbers dipping a lot in the summer, for the most part. In places like Minnesota and Winnipeg, there is only so much decent outdoor weather per year, and people spent it utside, camping, hunting, fishing, whatever. I know Winnipeg numbers dipped a ton every year in the summer months, as did the attendance at the monthly Civic Center shows.
Late August would be when the weather began to change into fall, and Verne geared his programs to begin in earnest around that time. The Blackwell-Brody feud, for example, kicked off at the beginning of June in 1984 at the big St. Paul Battleroyal, and Blackwell remained "injured" until the end of September. Brody, meanwhile, filled his time feuding with Jim Brunzell and Tony Atlas. In Winnipeg, Brody and Abby were around in April and May of that year (notably squashing the Baron and The Crusher in a non-title, no dq match), and then Brody was off the cards up there until November when he met Blackwell in their Winnipeg grudge return bout.
The Winnipeg April and May shows drew about 2600 and 1900, respectively, down from the usual 3500 - 4000 range. The numbers climbed back into and above the 3500-4000 range in the fall once again. St. Paul only ran a July show after the Battleroyal which drew respectably as it had Martel's first title defense against Bockwinkel on it (around 6500 IIRC), before running two shows in September, the first of which only drew 3000 for Martel-Rheingans and a Fabs-Heenan family Weasel suit match on Bobby's farewell tour of the area. Brody and Blackwell headlined the September 30th card 3 weeks later and did a much better number, before sellouts in October (Blackwell-Brody death match), November (Thanksgiving, LOD vs. Blackwell-Bundy) and December (LOD-Fabs, Martel-Garvin) returned the area to "normal" in terms of interest and attendance.
Something that should have been a tell-tale sign that things were going south to Verne was after the usual summer blahs in 1985 (1500-2000 a show in the summer, preceded by the 14000+ Star Cage show in April), the numbers never really rebounded from that range, with the exception of the 1985 Fall Battleroyal show, which saw the AWA and WWF go head to head with attendance being about even but still pretty high (10000+ at both shows). After that, they struggled. Without looking I know the shows were mostly below 3000, and the exceptions were not very much above that, and they never got it back. Hansen as champ, even programmed with incoming superhero Sgt. Slaughter, couldn't draw in St. Paul. Given the newness of Slaughter that was a VERY bad sign.
Winnipeg in 1985 followed the usual trend, holding a steady 3500+ attendance in the winter and spring, dipping in the summer, and climbing back up in the fall, and even beyond their usual numbers. The November, December, and Jaunary 1986 shows in Winnipeg all had above-average attendance. Vince getting their TV after the 1/86 show and taking over the Winnipeg arena was IMO a pretty substantial blow to the company as Winnipeg may have been their most viable market at that point.
....and, as I noted in the Territories thread, Vince never ran Winnipeg regularly and basically killed off the town because the local production the AWA did really got the fans to buy into the local storylines better than in most places. Their bouts and feuds were often unique, and the generic WWF material on their TV and occasionally at their arena did not appeal to the populace.
So yeah, AWA summer bad, AWA Spring-fall-winter good.