[yuriyuri]

Originally Posted by Columbine

Hmm, that's something.
Am I right in thinking that がほしい is used for sort of more long-term wants and wishes, particularly actions done for you, but it's not really used much?

So things like "I want something to drink" would be more natural as 何かをのみたい。As it's an immediate want that you can do for yourself.
Things like "I want to buy a car" can be equally 新しい車を買いたい or 新しい車を買って欲しい but i'd use たい maybe if I was stood in the car sales room and ほしい maybe if someone asked me what i wanted in general. You can use たい there as well though, can't you? But it sounds more like "Hey if you had a million pounds what would you buy?"; "I wanna new car!" as opposed to "I've been wanting a new car (for a while now)."

I've mostly only heard it used to describe what other people want though. Like you can't say ボッブさんは新しい車を買いたい。without it sounding a bit too direct and simple. So you have to say ボッブさんは新しい車をほしがっています
Wait? How do you say "Mr。Bob wants to buy a car" using ほしい？車を買ってほしがっています？買ったほしがっ ています？

てほしい is only really used for saying you want someone to do something.

新しい車を買ってほしい
I want (whoever) to buy a new car

I am not sure if you can use を with ほしい or not but I haven't seen it so far, maybe I am wrong though.
I mainly see it with が or with the が dropped.

You can still use がる with the normal たい form so:
ボッブさんは新しい車がほしがっています
Bob wants a new car

ボッブさんは新しい車を買ったがっています
Bob wants to buy a new car

I think the reason you cant use ボッブさんは新しい車を買いたい as a statement is because you can't possibly know the speakers actual feelings, and since たい expresses the speakers desire you have to make an observation of that feeling with がる.

This goes for adjectives like 怖い too.

You could however use 新しい車を買いたい as a quote or question etc.

I've probably missed some stuff, but I'm at work now so I can't spend much time on this post.