Have 9/9 and 10/10 potential spawn rates increased?

In practice this shifts the odds on a hunt rather than changing how hunting works. Potential is still rolled per spawn, so a top-score wild catch is still luck. You are just fishing in a better pond than before. How much better is not stated anywhere in the game, so plan a session around it being a nudge and not a promise. If you want a specific species at 9/9 or 10/10, expect to still be checking a lot of spawns.

The route that skips the dice entirely is Umbra Aniimo, also written as Umbrawl Aniimo. Every one of them has perfect potential stats, guaranteed, with no rolling involved. They are not something you walk into on a normal patrol though. Ecosystem nurturing is what gets you there: nurturing triggers wild surges, and a wild surge carries a chance of an Umbra spawn. So the reliable long game is tending an ecosystem and working the surges, while improved wild rates are what make ordinary catching worth doing in the meantime.

Raising potential after you have caught it

A catch that rolls short is not wasted. Certain adventure events, the Cross Tea Party among them, raise an Aniimo's innate or Initial Potential. You can do this up to four times on the same creature. That caps how far a mediocre roll can be rescued, but it means a good-but-not-perfect catch of a species you actually want is usually worth keeping and feeding into events rather than releasing and starting the hunt again.

Not settled: The increase applies to wild spawns, and nothing sets out how it interacts with the surge route or whether it varies by species, so the two paths to perfect potential are best treated as separate systems for now.