The idea was modelled off GTASC, so randomly selected bonuses was also on the table if we could think of enough.
Given my home situation and how close we are getting to the new contest start I'm going to have to put the bonuses idea on hold, at least for the first month. I'll be struggling to get everything all working in time as it is.
It's going to be awesome though - I'm adding things like tracking the daily leaderboard movements and timestamping when achievements are found, which can make some interesting data comparison or graphs later. I'm also adding more robustness to the notifications (the process that posts the unlocks in the thread here) so that it will retry ones it misses.
I've basically been rewriting the whole system from scratch; the original was pretty cobbled together, and I'm doing it properly this time with a common library and tests. I have the achievement selection and achievement checking parts working now, and just need to write code to handle the ranking (going to do most of it in code rather than use the spreadsheet now), updating ratios, and notifications. I then need to put some thought into how the historical information is going to work.