Is Prism going to harm US tech exports?

No it won't. The NSA just have to cooperate and send requests of behalf of foreign countries and all will be forgotten and for the greater good.

Every foreign leader will be delighted to have access to his nationals data.

If some country leader - lets call it Angela Cameron wants some info for the citizens under her rule - she just have to ask Obama for a favor, then the data will be delivered. The leader is not guilty of anything because the servers are in US and not in the nation jurisdiction and US will have no reason to not comply since these are not US citizens ... everybody wins.