Interesting this thread popped back up. Since I last posted, I've pretty much switched to two cards for simplicity sake:
Citi Double Cash Back 2% off everything, and I have a Wells Fargo Active CashBack (2% everything) on the way.
For a while I was doing the rotating reward cards but it got to be a hassle. I still have to remember to use my credit union debit card 15 times each month and I earn 3.3% APY on my checking & savings balance which adds up to more than any rewards card can give me each month.
Lately I've been getting a lot of $200-300 promos for signing up for new cards. The aforementioned Wells Fargo card has a $200 reward for signing up as long as you spend $1k in the first 90 days. I've done that with 3 or 4 cards this year-- Amex, BOA, Wells Fargo, etc. Sign up, collect bonus, wait the statutory waiting period, then cancel card. Also did that with a couple online savings accounts that give $250+ for sign-up. Sign up, deposit 10/20/25K or whatever, wait 90 days (usually), then cancel and move your money back. Even Robinhood, the online trading platform gave me $250 to put $15K there for a month, didn't even have to invest it. I've probably earned well over $1k just signing up for stuff, waiting, then closing.
I don't ever remember sign up promotions being this good or plentiful.