Look for pink/purple spice when picking a planet to terraform; don't bother colonizing to get anything else, it just isn't worth the time spent. You can always buy other spices cheap.
The T rating of the planet doesn't matter; once you get a high enough energy pack and the 4 terraforming tools, you can completely terraform a planet in one shot.
If you get bored with trade, there's a money cheat - I won't post it here, but it's easy to find via google.
I used to be an avid cheater, but I'm trying to get out of the habit of it now -- but later on when I'm "rerolling" a new race persay, I'll look 'em up. ^^
I initially was going after planets with green/blue, whatever color it is spice since it sells really well on my homeworld, but I'll try to find some pink and purple. The only problem is that most of the galaxy near my HW is controlled by evil people. SUCK. XD
The only problem I've REALLY been having with terraforming is I get the terrascore a fraction away from T1, and then it stops.. And I don't have the money to buy any more supplies, so it resets... And then when I finally got it, the game crashed and I didn't save! It's actually crashed several times now after I finally accomplished something. I swear, it's a conspiracy.