Tech trading is bad. Partly because if you head down the diplomatic tree you can’t fail to be making fabulous deals over and over again. The game is much more challenging and interesting without the constant need to go to the diplomacy screen every turn, scan through for new tech, buy it, sell it, make £’s, rinse and repeat. (If you don’t whore the tech then they do it anyway, so you might as well!). With tech-trading you get an equalisation of tech that makes everyone look and feel the same. Without tech-trading you get civilisations off doing their own thing: armour defences for one, beam weapons for another, planetary improvements for a third.
This means you have to think long term and short term simultaneously. Do you get those shields to help fight the Drengim or do I go for planetary improvements to keep up with the expanding economy of the Torians, or get some influence to cope with the Terran threat?
Furthermore you have to actually manage your early economy very tightly. No safety net of "just sell some tech" to get you out of a mess. It also means the trade goods are more significant as the only way to raise cash in a hurry.
It does take an element out of the game, but one that is so completely flawed when you’ve 9 majors and a few minors that it is a small price to pay.
Does anyone who wants a challenge actually leave tech-trading on, and why?