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

Potential is the stat ceiling you are actually hunting for when you sweep a spawn area, and a 9/9 or 10/10 encounter is the one worth stopping everything for. The practical effect of the change is that those encounters interrupt you more often. It does not make them ordinary. Treat a perfect-potential spawn as something you plan around rather than something you expect on a given route.

Finding one and keeping one are separate problems. Capture success comes down to which Aniimo Pod you throw, and success rates vary by both pod tier and pod type. That matters more now that good spawns appear more often: the worst outcome is walking into a 10/10 with only low-tier pods on you. Keep your best pods unspent for these encounters and burn the cheap ones on everything else.

Other reasons to be out in the wild

Ecosystem nurturing feeds into wild surges, and a surge carries a chance of spawning Umbra Aniimo. That gives you a second reason to work an area rather than pass through it, and it stacks with the better potential odds on ordinary spawns.

Legendary stardust yields and drop rewards have also gone up. So the same time spent hunting pays out more on the materials side, not just in the creatures you walk away with.

Not settled: The size of the increase is not stated anywhere, so you cannot plan a session around an expected number of 9/9 or 10/10 encounters.