I have a planet with a Precursor Elevator. When I colonized it, I chose the Neutral benefits to the PrecursorElevatorEvent. The +50% income I can see, but not the +50% trade income. Looking at DLC4_ColonizeEventDefs.xml, I see this block:
Other things that increase trade route income, such as PoliticalFocus2 and TidallyLockedWorld, use an EffectType of TradeRouteValueRaw and TargetType of TradeRoute. Should the PrecursorElevatorEvent XML do the same thing?
KrynnShadowTrade in KrynnTechDefs.xml also uses TradeRouteIncome, but maybe that is ok since the TargetType is Faction.