OK. let's go over these questions one at a time...
1) Noise can be used with Marbles in a number of ways, besides the point that it's useful for a number of other purposes...both modulation AND audio. But as an example, let's take the "jitter" input. By introducing noise at varying levels through this input, you can increase the instability of the Marbles. But there are loads more possible than JUST that. Suffice to say, noise is pretty essential in general in ANY synth, and there's tons of points in the build where a totally random source of that sort would be useful.
2) By using the Penrose quantizer. What you'd do there is to define a set of notes that fit the overall musical scheme you're working with at the time, then feed a modulation source into the "Input" and a clock pulse to the "Trig". The trigger fires the sample and hold circuit in the Penrose to lock in a single voltage value from that modulation curve, then the Penrose "rounds" that value to the nearest assigned scalar step. By using very sparing clock pulses (Skipper at, say, 3/4th of maximum stochastic skips) to add harmonically related blips every time the voicing connected to the Penrose fires.
When you consider what's going on there, it's really very sample-and-hold-like...but the resulting control voltage values get constrained to ONLY the ones that you've defined, not totally random values.