The hp increase is about 100 or so. Might increase more with leveling the wyvern up. It just p*sses me off when I think about that weapon. I was fighting one of the new birds in Marjami Ravine and it was ping-ponging back and forth between me and my wyvern because this sh*tty spear couldn't even do enough damage, on a piercing weak mob no less!! What's more, war and drk get another GS and GA when they already have two great options lol and drg only has a weapon unobtainable by most.
Edit- Taken from someone on BG. This is with Upu though so 6 lvls higher then sh*t spear.
Ranth: 110~156 damage per hit for my wyvern on a Blanched Mandragora outside Adoulin. 1132 Flame Breath with deep breathing (and to my knowledge) all available breath damage/enhancing gear. 201~240 Critical Hits on the mandragora, it was only hit for about 30~35 damage from the mandragora and evaded a lot of its attacks. I don't think this is going to help enough in that it'll be a relevant source of damage anyways due to the breath damage reduction making wyvern breaths garbage anyways, but I guess it's better than nothing.