I do all my ads around a price promotion. What works for me is to do promos at 6-week intervals, and to schedule ads to run on different days of the promo.
Yes, it's hard to tell what's "spill-over" from the previous day's ad, but that's OK. I just figure I'll throw all my marketing dollars on that 5 days or whatever, and go for it, using the sites other people seem to have had good luck with.
I don't do ads around new releases. instead, I promo an earlier book in the series once the new book has some reviews. That's worked great.
Your alternative scenario sounds good, but I think what you'd miss out on would be momentum. The very thing that makes it harder to measure the effectiveness of any one ad is what could drive your sales as a whole--the synergy you get from a bunch of different ads around the same promotion (or whatever). Yes, some people will see the book promo'd in several spots, if they subscribe to multiple lists, but that's a time-honored marketing truism--that you have to show people an ad more than once to get them to act. So that's all good.
My 2 cents.