Is there a possibility to "slow things down" in the presets of my choice?
No, not in general. It may be possible in individual cases, but I personally would not attempt this except maybe for presets I have made myself and I know the code.
When talking slow and oneiric presets, you might try the work of Amandio C. on this forum. Unfortunately he did not bother a lot about beat detection and most of his presets are just moving at a constant rate.
You may also find something in my own presets. Some of them are frantic, some deliberately slow, depending on the music I listened to when making them. I'll attach the entire collection here, including the old ones which are already included in the milkdrop distribution; just try the newer ones, I have learned a lot since. It's not many presets in total but very different in style and motive, and some of them took me months to write. Pixies party in particular can be adjusted to any particle / camera speed you like.