The best buff the spear could get is an unguided mode
The main weakness of the spear is that you are forced to only be able to fire it whenever you acquire a lock on. But as we've seen with the warrant and the missile pistol both of these weapons have an optional unguided mode which gives you extra versatility to switch things up when the situation calls for it. I propose giving the spear an unguided mode so that just like the missile pistol it can be fired in closer range.
This would make the spear a lot more viable than it currently is. With this change if a charger or Hulk got too close for comfort you could still kill them in close quarters unlike currently where after a certain range you can't lock onto them because they're too close to you making the spear useless.
This would also allow the spear to be able to blow up bug holes and other side objectives not to mention making it way more effective at hitting weak spots on heavy enemies such as the eye weak spot on the factory Strider.
Overall it would just be a solid change that would give the weapon a lot more flexibility in how we use it and it's a quality of life Improvement that would drastically increase the viability of the weapon without changing any stats on it. It would be balanced and wouldn't make the recoilless rifle useless due to the fact that the spear rocket in unguided mode could be made to travel slower similar to the missile pistol not to mention that the spear has one less rocket than the recoilless rifle. If a missile pistol can do it why can't the spear?