I don't see it that way. If they're already researching the tech they're going to get it anyway, so I may as well make a bit of gold out of it and improve my diplomacy while I'm at it. If however they pose any sort of military threat or rivalry, or the tech allows them to build a Wonder I'm currently working on, then I'll make them wait those extra turns.
This is pretty much how I play it. If I'm considerably more advanced, I will especially milk my weaker friendly civs. If they are civs that are closely linked with my principle threats. . .no way.
The game I'm currently playing has been considerably different compared to others I've played--I destroyed Rome as a nearby civ on like the 10th overall turn (no defenders in Rome, just Nero fiddling

Come to find out the nearest civ's continent was a couple tiles away but they weren't very advanced, either. It took til about 1100 AD until I had contact with 5 other civs.
Surprisingly my score was 3rd when I had a number of competing civs revealed, and I'm on the verge taking over the top spot in points, but I still have a lot of catching up to do, and I'm just now becoming financially solvent at about 1700 AD.
It was quite interesting seeing the tech-trade aspect from the aspect of trying to catch up.
(which will hopefully serve me better for trying more advanced levels of play).