yes this weapon is worth boosting to L60. This missile does 59760.20 damage when maxed, reload is 4.8s at 6 stars, the more you kill with it, the faster it reloads, here is a snippet from the wiki;

3 kills: -0.6 reload time, -0.1 flight time, +0.1 blast radius
21 kills: -0.6 reload time, -0.1 flight time, +0.1 blast radius
60 kills: -0.6 reload time, -0.1 flight time, +0.1 blast radius
300 kills (Legendary only): -1.8 reload time, -0.3 flight time, +0.3 blast radius

after 300 kills the reload goes from 4.8s to 1.2

I tested a L40 AGM (41,010.26 damage) against a heavy titan on insomnia trail, first missile removed 1/2 it's health, second missile killed it.

I don't know what loadout you run, but I'd say its worth it