Mmm, I'm on JellySlayer's side of the issue. At first glance, yeah, maybe making mundane monsters less homing sounds nice, but I think it would slow down the game more than you expect. It's not just live-sac'ing that would be broken - characters would level slower, the game would take more time, etc etc - it affects a LOT of thing. Background corruption, item quantity, and hunger would also be affected in an ancillary manner. Everything homing in on me no matter where I am definitely seems wrong to me, but I think it is the lesser evil of everything ignoring my presence on the level. I think that would be more frustrating in the long run.
I do, however, agree with the lot of you on invisibilty. Monsters seem to have a pretty uncanny ability to find you when you are near them, and attack/follow you even if all you did was walk within one square of them. I don't know if that would be an easy fix, though, and patching that issue would come at a cost I'm not sure if it's worth.