Everything was good until a few days ago when I picked up the pot and looked under ...only to see some extremely small (yet still visible with the naked eye), white bugs moving around very rapidly on the bottom surface of the pot...as well as on the saucer.

I just about froze in place because the Peace Lily was sitting about one foot or so away from one of my fussy, drama-queen Africa Violets, now in bloom.

Of course, I care about the Peace Lily just as much as I care about the AV-s.
I isolated the plant immediately, I sprayed on the outside bottom of the pot, the leaves, as well as the soil with "Worry-Free" (insecticice and miticide) and I took it to the garage.

I waited about a week and today I did this again and watered so it will force the insecticide inside the soil. After the first episode, I no longer saw any trace of those bugs...which I don't even know what they were.

I never saw them on the surface of the soil or on the leaves in the first place...just under the pot and on the saucer. But given I haven't re-potted, I still don't really know what's inside the soil. No traces on the outside, in any case.

Overall though, the plant has been starting to have less lush leaves over the past few weeks. They seem to be getting smaller ans narrower...it has browning tips and just does not seem to be as happy and impressive as it used to be.

I don't know if this is because of those bugs (could they still be in the soil?), or because it needs re-potting in a slightly larger pot (I placed it in a relatively small pot from the beginning).

I just don't know. Given the story and what it looks like now...what would you advise me to do?

Re-pot now, in the Fall? The plant added quite a few stems since I got it and it seems quite dense now. It also looks like it asks for water much quicker than it was doing in the beginning...and even after I water it, it doesn't seem to regain its really lush and proud shape anymore. It's not wilted, but it's not strong and lush either.

I was planning to do re-potting in the Spring but it looks like I might have to do it now.

I should note the plant usually sits in my living room. In the pic, I took it outside to spray.
Any advice would be appreciated.

I don't think the insecticide did anything because the plant had started to look less than hot before I used the insecticide. Besides, the first time I only used it on the leaves and top of the soil - after I watered.

It was only today that I used the insecticide inside the soil, by watering it in after spraying. I wold rather think that whatever little bugs I had found on the saucer is what caused the plant to lose its overall healthy look.
Either way, it looks like it 's repotting time.

According to sources on the AV Forum, AV's are susceptible to soil mealy.
Hopefully, mealy isn't the problem, but it's something to consider.

Begonia, your S. Domino is lovely...Toni

I doubt it is mealies because those are white, fuzzy and move very slowly. These were really, really fast and not fuzzy. Besides, my AV-s are perfectly fine right now. I was afraid that they may catch whatever these bugs are from the Peace Lily.

May I ask you what is "S. Domino"? :-)