afaik income is a multiplier of tradeports on a trade-chain (planets with a tradeport next to eachother using the shortest travel-time possible
the longer the chain, the more income you get, i dont think it's related to tradeships dropping of goods
(if would be related to tradeships dropping of goods, then it would drop of depending on flight time or jumps, and a steady income would become buggy and unreliable.)
tradeships that get destroyed do give the empire destroying them money, and reduce the unfortunate owners income ... until it is rebuild
phase stabilizers are already extremely usefull when it comes to tradeships, i.e. they wil not have to traverse neutral ground to get to another planet so the chance of them being destroyed is much, much smaller (not counting interstellar trade)
with buffing the stabilizers.... i dont think that's neccesary... and isn't realistic,
there's a reason star to star jumps are used, they dont use phase-lanes for it and phase stabilizers create artificial phase lanes