The only stages left that didn't get to 999 are All Mixed up and Penny's Mix. Dare to do the challenge? Highest score in All mixed up is 849 and the Highest score in Penny's Mix is 676.
I recently got this game as I had played Smooth Moves in the past (never got past Mona's stage because my Wii's sensor bar is too finicky for games like these), and wanted to grab GiT to see if I could finally beat a WarioWare game...and I actually did. Fully completed the story (and currently in the process of getting all characters to Level 30). However, I had to spend a few Wario Coins to keep myself from having to repeat everything again. Most of the ones I spent were used during Dr. Crygor's section, and the rest went to the final segment with Wario. Keep in mind: until then, I had not ONCE had a Game Over in the story. I lost a few lives, yeah, but I didn't lose all of them in the story until Showdown. Considering you only get one mistake, the fact that you were able to get the score to cap out in the Showdown is actually worth applauding. You are the king of WarioWare, my friend. No doubt about it.