As a simple upgrade, Bigger Globs serves as a way for the Glue Gunner to circumvent one of his greatest weaknesses, a lack of effectivity against groups of bloons. By increasing pierce by one, it allows the Glue Gunner to effectively double his influence at less than half of the base cost. It also serves as a stepping stone for Glue Splatter, an upgrade that is considerably more effective as well as considerably more costly. For an early game, using this upgrade instead of its superior version may be the more viable option if money is low.
When considering following Path 1, it seems obvious that increasing targets hit per shot is much more favorable than greater slow time and effect, since bloons will be disintegrated before those factors become beneficial. It also lets MOAB Glue double in dealing with M.O.A.B. Class Bloons in the short-run, making it better for slowing several MOABs simultaneously versus slowing the MOAB and its children.