If you suck at fishing and plan to use EX Bait, then yes, get Mooching.
If you're relatively decent at fishing [or cheat], you will not need it to catch anything. Matsya being the only thing people really use EX bait for anymore, are fairly simple to reel in without Mooching.
Rings are more worthwhile, if you need assistance. Especially since Drill Calamary would be a huuuuuge waste of time in comparison...