Since I normally play without the point counter, I try to gain as many VP as possible before ending it -- just in case I miscounted along the way. And if I'm having a KC/Bridge/Goons megaturn, then yes I'm going to buy everything I can, in excess of what's necessary to beat my opponent, because I can be proud of it (and I'll get achievements on Councilroom, haha).
As for taking extra turns, if I see an opportunity to end the game and win, I do. If I'm not confident (like 60% sure) that I'll win by ending the game immediately, I might prolong it in the hopes of setting up a more certain win, depending on whether my opponent's deck has a better chance of coming back and beating me.
Especially when I'm playing normal games on Iso, I try to play as quickly as I reasonably can, only pausing to count VP or cards in deck when it's critical. If it's a tournament or something, then obviously I'm going to take longer and expect my opponent to do the same.
I basically only get annoyed when people hold out to the point of timing out. Actually, if it gets to the point where I can make them resign, I just figure they disconnected and click it right away, unless they gave me some warning in advance.
I think that's pretty fair overall.