Does increased planet quality worth the 8 point pick?

It will add usable tiles to every planet.

No

To my understanding it only increases your starting planet's tiles. It raises the PQ of all your colonized/captured planets, but does not add tiles

It does add tiles to your planets, but only to ones that you colonize.

#3 is correct. Makes sense if you think about it. If it added tiles to every planet, especially those you capture, you would end up with an infinite upper limit.

My 44 tile non-home planet covered in neutrality research centers makes me think it's worth it.

Each planet adds tiles when you conquer or colonize. For example you attack a 12 tile planet. When you occupy it instantly becomes a 16 tile or thereabouts.

I know that with the smaller PQ bonus (10%), I ended up with class 49 planet. It makes me wonder what the highest anyone's ever gotten is.

There is no limit as far as Ive seen, getting nutrality doubles all your PQ you can go well above 100.

ST

personally I do not care about the PQ... I only care about the usable tiles.. the most usable tiles I've ever had were 26.. the PQ of the planet was 39...

No the only PQ enhancement worth getting if you really have to is the +10%.

Reasoning behind this: -

+10% = 3 picks
+20% = 8 picks

Therefore the best points to increase ratio is the +10% as the +20% is more than double the points.

in a word, YES it's always worth it. It's a simple calculation, lets say u have a class 8 planet ripe for colonization. if you have a 20% PQ bonus, that means: (8 * 0.2) + 8 = 9.6 (10). Meaning that planet will now have 10 tiles to work with instead of 8, that's 2 more factories. The larger the planet, the more tiles you get. Take a size 16 planet, (16 * 0.2) + 16 = 19.2 (19), meaning you have 3 extra tiles. TILES ARE WORTH THEIR WEIGHT IN GOLD. Some peopel will say, but hey! you could have a 20% weapons and defense bonus! OH BOO HOO! Just mine a darn weapons resource fully and you can have a 50% weapons and defense bonus instead. So hmmm, 20% bonus to weapons and defense? or extra tiles for more factories, or stock markets... HMMM... simple choice in my book.