1) You start gaining Philosophy Tomes as early as Stone Vigil (each SV run is 20 Philosophy) which is Level 42.
2) They are adding the Philosophy Tomes and Mythology Tomes to other dungeons (and hopefully Cape Westwind) with patch 2.05 (Tuesday).
3) If you get a good group of 5 DPS, 1 Tank, 2 Heal you can Speedrun Praetorium in 30-33 minutes. This is approximately equal to, if not faster than, CM.
4) We'll just have to wait for patch 2.05 to know what's really been changed or added.