With premier of DR we got Ship Upgrade Token to modernize ours T5 ships. It was kinda useful for old players, but now new players rather to upgrade their T5 goes for T6 directly and Token starts to be useless which is sad because all work that was put in creating it.
How about expending it for other tiers, not only T5 -> T5-U. Why not let players to upgrade ship they like from T2 up to T6. If player want to upgrade his/her T4 Tactical Escort he/she would get option which T5 escort (Patrol or Advance) stats she/he want to obtain. Of course upgrades could be done only with compatible classes: Cruisers to cruisers, sci to sci, etc.
That way we could keep old ship skin with new stats (which will probably make Galaxy fans very happy as they could fly Galaxy-looking ship with useful layouts)
Possible upgrade path:
T2 -> T3 -> T4 -> T5 -> T5-U -> T6
As for $ thing, simple solution is to make T5-u -> T6 upgrade cost for example 4 Tokens (2k ZEN in pack) + 1 to upgrade from T5 to T5-U which in the end gave little less profit from one change then buying whole new ship, but more people would be will to get ship that way, which most probably means bigger final profit.
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