I was experimenting with this to discover what's happened under 1.1. This is what I discovered:

1) The ability now works on worlds you colonize and not just your starting world.
2) The bonus does not apply to planets you conquer.
3) It doesn't QUITE work as advertised. You will get the 10% or 20% initial boost. However, things work a bit differently once you have researched up to terraforming. For Earth, for example:

Ability-Base tiles-tiles when fully terraformed
No PQ ability-10-13
Green Thumb (10%)-11-14
Magical (20%)-12-18

So it looks like the ability affects both the initial number of tiles AND the number available after planetary improvements. This would also explain why Green Thumb costs just 3 ability points whilst Magical costs a whopping 8 rather than the 6 you might expect...the benefits are potentially more than twice as good.

5 extra tiles on an average planet is definitely worth 8 points IMO If you're playing against a small number of opponents with some high quality planets around. It's not so impressive if you're playing a large number of opponents though since you'll not see the benefits on planets you take through conquest.