Board Thread:Event Discussion/@comment-9522002-20130518225437/@comment-5945589-20130519044450

For tower ranking... its all up to luck. You can climb for miles but not meet any WG (the main source of your collectibles). You need to keep climbing, and hopefully meet & defeat as many WGs as you climb.

Generally, if you intend to reach the top of the tower without spending, you'd have to forget about rankings and start climbing from the moment they say "GO!!!!". It's your call.