If you like slayer keep the spear. Even if you get your summon to let's say 68 for a bunyip, guthan can still be usefull. Also I have spend an estimate of 3.5M to get 64 summoning now (buying both second and shards). I think it'll cost me like another 1.5M or somethin to get 68. So It's about 5M I think to get from 1 to 68. Anyway, I have to say I love my guthans in lots of spots when I do slayer.