I also think in general that no matter how much Hillary spends, she faces the law of diminishing returns because there are just very few people that are still persuadable about her. Trump, though, has far more upside because he's had everything including the kitchen sink thrown at him and he's still either statistically tied or ahead (and likely FAR ahead in reality). I believe that there are far more people who are persuadable regarding Trump, and many will be persuaded once they see who he surrounds himself with and realize that he's not the bogey man.
This is the first election in which the Internet has become a major political force, which means that dollars spent on TV ads are demonstrably less effective than in years past. Between the flood of alternative information sources (Facebook, Twitter, YouTube, Instagram, blogs, etc.) and the combination of cord-cutting and Tivo-ing, TV ads just don't offer the ROI of years past.
Of course most modern campaigns are staffed with media consultants who are really there to push ad-buys, so it's no surprise that Hillary's top-heavy campaign is all-in for the tried-and-true ad-spend model of campaigning. Trump is a different animal and understands the social shift and how a tweet can now be more effective than a million-dollar ad-buy in several states.
I expect plenty of Trump ads for insurance purposes, but he's not going to waste money during the Summer when nobody but the talking heads are paying attention. The real ramp won't happen until after Labor Day.