Well maybe not much, but at least a bit. Ok, no ship trades is a good solution also
But no tech trades allowed is what I regard as the absolut minimum standard. With only ship trading allowed, you have to build the ship, trade it, move it to a shipyard to analyse, do the analysis - more time, not the otherwise possible instant exchange. Plus, you cannot ally tech-wise with someone from the other edge of the galaxy, and are limited to those who are near to - a natural, "healthy" limitation.
Of course, total dedictation to an alliance might lead to building shipyard-colonies within the other players empire to facilitate these trades. But these kind of alliances, from start to end at all costs, are another problem - I also think alliance victories should not be enabled. I favor Last man standing, where you have to beware who you are working together with and how closely.
Alliance victories possible and tech trades allowed reduces the game to a kind of "how many friends can I get together into this game". These kind of games are team vs. team in reality and not player vs. player - whoever wants to be the lone wolf there will surely loose if there is a minimum of competence in any team.