1) No, Carrion Creepers are a weird, weird power. The enhancements won't propagrate to the damaging creepers themselves (because they are a pet of a pet apparently), all its worth slotting them for at the mo is Recharge.
2) On Plant / Thermal I'm not so sure. Thermals shields are Resistance so PB won't affect them, but it will affect Heals. PBed Seeds would be nice too.
3) Plants AOE Cage does double the damage of any other (with maybe the exception of Fire), sure that's still not massive damage but its something. You also get Seeds which is an amazing power, really early. So there are strengths there too.
1: Acc and Dam on carrion creepers don't work. They do lots of damage - just in small ticks.
2: I'll tell you on my planty when I've got it 
(I'm thinking probably not).
3: What do you mean minimal damage? The damage of Roots is double every other controller AoE other than fire - meaning that spamming roots often does more damage over time than an Electrical blaster spamming his AoE does (see my plant/storm guide for details). Seeds of Confusion can eat entire spawns alive on its own and provides very good aggro management. And Carrion Creepers again does low damage per tick - but the ticks add up when you've got about 9 creeper vines wacking half a dozen targets (and you didn't even need to cast it in combat).
What's probably confusing you is the small size of each damage tick - plant certainly has no shortage of total damage output, especially against large spawns. (IME it's just as fast to take down a dozen lieutenants as it is to take down one with plant - and no more dangerous if they start bunched up).
Just to put the numbers into perspective, one hit from a carrion creeper vine does about 30 damage, two thirds of that toxic (the least resisted damage type of all IIRC). They'll get three attacks over the course of their life for 90 or so damage (now we're getting somewhere). Say 75 allowing chances of missing. Half the mobs spawn a carrion creeper - 37.5 damage per target per ten seconds. Doesn't sound like much, I'll agree. But that adds up - ten targets give an average of 375 damage on a 10 second cycle from one cast of the creepers, and the damage cascading if it kills one mob. Throw in Roots and Melt Armour (or freezing rain in my case) and most blasters have a hard time keeping up with your total damage without nuking.
And the best thing about Carrion Creepers is that they form no part of your attack chain (following you around as they do) and can be cast from round corners.
I don't offhand know if plant or fire does more total damage as a controller set but for AoE damage the two are comfortably in the lead and nipping hard at the heels of many blaster sets. And Fire doesn't have Seeds of Confusion - which is an absolutely monstrous control.
Thanks both and nice to finally know how carrion creepers work.
Freeing up powerboost would allow me to get one epic armor and invest in teleport to make audrey go where i want her to go. My question wasnt if its a good power for plant. I wanted to know if it was worth it to augment my heals even though i cant fit in hasten and thus can´t cut the recharge on powerboost that much.
1. Carrion creepers seem to do loads of damage in the in game info but the damage seems minimal checking all parts of it on red tomax. Is it worth slotting for damage?
2. Is Powerboost worth it even if you cant fit in hasten?
3. Is there some reason why plant is weak compared to the other sets? No dropping fliers cant target stuff in air and no secondary effect along with minimal damage, long activation times etc.
I like the massive control but grav and earth also have nice control with some nice side effects.