Same. It's all about getting used to your units and the timing of their attacks. Switching in someone different, such as Arlong, can really mess with things if you're not comfortable with them. I think I've, more-or-less, gotten used to him though. I can even switch between targets between attacks [if I need to] to better utilize an enemy's weakness. I can one-shot the crab on Elite Buggy if I get a QCK Orb with Ace and use him in the last string of my combo. It definitely helps speed things along.
But yes, if you're farming Elite Buggy now there really isn't anything else left to do. Don't give up yet, however. Keep up the farming, since the level gives decent XP and it's a benefit to increase your Pirate Level so you can gain more Stamina as well as Unit Cost. Not only that, but with other upcoming events, you'll want your units to be as high a level as they can be, so the XP turtles in Elite Buggy will give you that added benefit.
I only wish Cola dropped more frequently. I've already failed three times on my Going Merry. That's 17 wasted Cola.
In-regard to the percentage of boss drops, it's pretty low. Maybe 5%? Possibly even lower than that. It's worth it for some [such as Zeff] who doesn't currently have their own event island, but for others [such as Arlong/Kuro/Alvida/etc.] I'm waiting until their respective events [unless I have nothing else to spend my Stamina on].
