You're forgetting to factor in that every Elder Collector has its production raised by proximity, up to a 1.4 multiplier.
At Mag 4, every +10% increases the successes generated by each Elder Collector by +1.6 per turn. For Mag 5, the value is +2 per Collector per turn. With Worm lvl 3, the average successes are raised to +2.4 and +3 respectively.
If we intend to have Worm lvl 3 and 10 Elder Collectors by the end of turn 2, then 1 extra proximity will give at least +48 on Turns 3 to 4 from bonus Collector production alone, and +16 from bonus growth action successes, for +64 total. Subtract the 30 cost of the Skimmer, and that's +34 net. I'm really not kidding when I say a Skimmer bought now roughly matches or exceeds the value of one Collector.
And since the Elder Skimmer also gives 4 auto-successes to movement per turn if a Course is decided: