Just finished the entire game today actually... there are a few parts in the game that made me want to throw something at something else, but I refrained. It's also very gratifying once you beat those frustrating parts. And yes, the purple coins on Luigi is probably the hardest part in the game IMO.

 Thanks, though nevertheless I'm sure you will beat the Bouldergeist Daredevil mission some day.  Feel free to ask for advice though if want.

I beat him second try, an I'm generally known for sucking at games...

I find it funny when some people say that Luigi's Purple coin in the Toy Time Galaxy is hard. You just jump from coin to coin. Don't get all at the beginning. I beat it on my first try everytime. ^_^

IMO, it is one of the easier purple coin challenges. 

funnily enough, I killed him in my first attempt losing only one slice of the pie. The daredevil run I then perfected it, killing him in my first attempt. I didn't really think this was a difficult boss, and I'm certainly not some sort of game playing prodigy, I'm average at best.

I didn't really find him that difficult. Most of his attacks can't really hit you. His flying boulders are easy to avoid, as are the attacks with his hands. Just about the only thing that can hit you is when he creates the lines of boulders, but you can see them coming quite easily, and break them if you get trapped.

There were much more difficult bosses, imo (that damn mole in gusty garden took me a while)

EDIT: oh and in the realms of non-boss fights, can I just say that the candy galaxy was bloody hard! my god, never have I died so many times on one level. I can't believe they put that galaxy so early.

If you want the game to be challenging, than start competing for speed run times.

 I just run in a circle around him.  All of his attacks end up going where I was a second or two before.

I must admit that I partially agree with you - SMG could have used a little more difficulty. On the other hand, I know several people who will never manage to get all 120 stars. Literally :P You gotta face it, you and me and many on VGChartz, we are probably somewhat "elite".

And you should admit that, while a little too low, the challenge of SMG is very well done. No quest is ever unfair, any gamer will be able to at least know what they have to do. Some of the truly hard games I played in the past were just unfair and frustrating, by today's standards. I wouldn't wanna replay TMNT (NES), for example. Currently, I'm playing Zelda II on VG, and I'm having a hard time motivating myself to start over and over at the damn temple.

luigi's coins... ZOMG! I remember I had a difficult time getting the 5 silver stars on Mario, collecting those coins is going to be impossible.

And Dreadnaught coins... suffice to say there were only like 10 star bits in the entire level but I had over 400 by the time I finally got that star (and I shot quite a few of them)

The key is not to get nervous. You don't need all the coins, just jump along, there will always be a platform in your reach.