Minor Pedantic Point of Contention: Quake 1 had the rocket jump "discovery"; by Q3, it was an expected part of the gameplay. However, this does not affect your argument in any way.
It's nice to see such parts of gameplay emerging from simple bugs. I would argue that it's much more rare nowadays, with games which aim to be always more realistic, and blocking your movement.
Not really sure what you're talking about. Rockets and grenades hugely impacted player speed in Quake 1, but not so much in Quake 3. Check the speed run of the following level to see what I mean:
http://www.youtube.com/watch?feature=player_detailpage&v...
The quad damage'd grenade jump at 11:19 is mind-boggling. I don't remember seeing that in Quake 3.