I did! Mintyfish is at level 503, with strength and defense just above 750. I did move HP up to 1008 but I don't think I'm going to push it to 1500.
There's no increase in multiplier after 750 for strength or defense so one could safely stop at level 375, but because I had put HP at 840 on my own, I had to bring level up to at least 420 in order to do anything with strength/defense. Once I did that, I made a goal of getting to level 500 to be able to get the last level of faerie abilities. I'm collecting my bottled faeries for it now.
I should mention that by the end, I'd invested into Faerie Quest Fortune Cookies, so I spent the last few months doing a faerie quest every day (sometimes twice - thanks faerie festival!) and upgraded randomly for much of the way and trained to even things out. To be honest, the FQFC path was more fun than the full-time training grind, but you might have to spend real life money for it. There have been in-game gifts of NC lately and I happily spent it all on fortune cookies.