[gold stinger]

It doesn't come down to question of what type of note you're hitting, but rather how fast the song is. You could have an extremely slow song that works with 32nds, but can't figure out how to play songs with a tremendously fast speed, like Max300. usually 32nds that are too fast will be changed into what we call a "Jump-Trill" or something of the like, where 32nd notes are changed into quick jumps, which is what I believe you're getting at.

Back with your original question in mind, time and practice is key to getting better. Focus on problems you might be experiencing while playing, (like hands (3 or 4 notes at the same time), or jacks,) and progressively give yourself harder challenges when you feel that you're up to it. Playing spread is much easier than trying to play index or one-handed on the harder files for sure, but that's because the learning curve of getting better is generally shorter when playing spread, hence why most people play it.

Although, there are some people in this community who have became extremely good at the game, better than a lot of others by just playing index or one-handed, but if you're going for "training" your fingers to go faster than 16ths, I think making the switch to spread would be a good option to take if you want to get great scores on generally harder songs.