Myself, I've got my 6 cities in dwarves-fairies and just got to lv10 MP on my main city. Strategy was to basically check in every 3-4 hrs religiously, go for mostly time boosters on the chests and lower cost chests whenever possible. As I progressed through the event it seemed that I wasn't having insurmountable time/production issues so I also took a few 85 coral chests to get a chance at the 8hrx4 boosters, the corals or the daily prize. All in all I'm doing tolerably well and on track to get to lv10 on most of my 6 cities. I have doubts that 1 or 2 of them will not get beyond 8-9, but pretty happy overall. In lower chapters I would often have a farm to make productions ahead, but this time with all the space crunch involving guest races I couldn't do much of that in more than 2 of my cities and only in one of my cities was I able to make a bunch of lv1 tier1s manus simply because I had not placed all of my guest race manus at that point. I didn't buy any diamonds, but I did luck out for once and got some corals in a MO in my MA! =D
update: Today I got a second city's MP to lv9, but I have burned through an insane amount of time boosters and have almost none left for after the event the way it's going. It's making me think that one of the main effects of this event is to make all players burn through their stockpiles of boosters, unless they want to buy/spend diamonds. If that is the case then I would suppose that the event is a success from a business pov. My lowest lv MP is now at lv8 so I still have a snowball's chance at getting all 6 to lv10 before the end. A new development is that for the first time ever I earned a second event building from the prize rotation. I expect to frag it, but will wait and see. Still fairly happy with the event as I have gotten much more sleep during this event and gotten much done to advance my cities...so thanks to IG for that! =D