There will be a promotion (possibly tomorrow) to buy SK at a much cheaper rate. It always happens.
Yes, I heard about this. However, I feel that Inno should get some money for making this game, and that EUR20 is just a small part of what they deserve. At this point, I was already considering the idea to sometimes buy diamonds to this goal, despite that I never used them until now. So I bought the diamonds / SK I needed at the current rate, and am not sorry at all.
Are you suggesting that taking one beacon makes it less likely to appear the next time. I think that's some advanced computations that Inno is unlikely to wade into, even if they saw a benefit.
In this case take the 89. It's not a bad choice. Avoid 30 and 54 like the plague if you want the staffs.
I maintain servers for almost two decades already, and have sometimes seen such advanced computations to predict and direct users where I wouldn't expect them. So, I just don't know what Inno does or doesn't.
30 usually gives 1 point (30 SK / point), 54 gives 2 (27 SK / point), and 89 gives 3 (29.66 SK / point). 30 and 89 usually offer better chances than 54, but I almost always was interested in obtaining the complete set, so I went for the best SK / point ratio - in this case, 54.
The result of this strategy appears good: I am a new and inexperienced player, and during the first 10-15 quests had a wrong impression on the event mechanics, resulting in bad beacon choices. Also, I don't remember having luck with chancing on extra SK. (Except that since I bought all SK I needed and spent them, I chose 3 times more with the remaining SK, and hit the 80 extra SK twice!
). I bought the equivalent of about 22 points. Those put me into the Silver League; without them, I would still be above the average for the Bronze League.