Well, i wrote that alot of times already, and people above just wrote that too - it mostly depends on the type of teh event and particular Event.
I have no idea how you guys manage to get high rankings without wpending anything and not even playing too much...
I'm total f2p, a maniacal homestuck otaku that spends all his life on games, and can spend up to 30-35 hours contunuously with no sleep, playing some game during the time-limited event, if i get addicted to some online f2p game. Right now my top-addiction is PPS. So, during the last Gambit i'v played it from day one (night one to me, since i live in Russia and in PPS daily quests reset on 02:00 AM and daily login bonuses are given out at 03:00 AM), skipped sleep like 3 times during the Event, and always keept a laptop near me with PPS running on it, while i play different games, so i never waste any Stamina while it's full.
Even trying that hard, the last Gambit only gave me about 30k Stamps, no matter i always picked N SECs right after they bacame available, ant levelled them up to lvl 100 before doing any rolls, so all the Stamps i get had bnus from Slayers, and i even got one R Slayer during the Stage 2 of the event. So, with new "no glasses" rule i had absolutely no chance to get 50k Stamps reward SR, And for the rating - i only cared for the EP rating and failed to kepp up in top 1k to the end of the Event, even by burning all "temporary consumables" at the last day of event (i managed to make it into 1k, but just had to go to sleep after another 30+ hours play session when i was around Rank 900 and there was a few more hours before the event end. - of course, when i woke up the event was over and i was rank 1073. Almost the same crap happened to me few more events before that, but those times it was my fault, since i didn't yet knew how Events work and what is the Time Difference (som for example, i once thought i have sevral more hours - almost half a day, actually - until the event's end, and was just about to reach the required stats to get the reward, and had more than enough temporary consumables toachieve that, but then suddenly it turned out that event ended much earlier than i expected, leaving me with no reward (and once i even won and SR card before the event has ended, but forgot to take it out the GiftBox before the even't end, and after the Maint. on Event's end it was gone, so i never obtained it.
While, of course, having around 700, or 450 SED that i had before this event, when i used up all my accumulated R, SR and Ex Wildcards, lets me win all SRs that i want on most other Events - which, often, require getting in that 1k main even't rating...