I have spellweaving on one of my tamers and I've only reached 40, but I intend to take it to 110. So far I've only used it while working on taming, so I can't attest to its usefulness in pvm or pvp, but I know several fellow tamers who have spellweaving and it seems to be very valuable to them. The Etheral voyage spell is especially good because it allows you to walk around without aggroing monsters. There are also several useful spells that will heal and cure you ask you take damage and get poisoned and even res you if you die while the spell is active.
My tamers template (when she's finished) is:
Magery 110
Eval 110
Med 100
Taming 95 (higher with jewels and talismen)
Animal Lore 95 (higher with jewels and talismen)
Vet 100
Spell Weaving 110