2 SMPS - Does it make sense?
I've used multiple SMPS in these situations. They're called for when power efficiency is the main concern, noise a lesser concern, and the power needed for each voltage is within a magnitude.

Your question, however, says that noise is the main consideration, in which case I wonder why you're bothering with SMPS at all. If noise is more important than efficiency, then don't use an SMPS at all and live with the high power requirements.

Now, if you want to do this right, you need to start from your load, and the signals within, and do a proper noise analysis, with the goal of defining an acceptable level of noise. Then work this back through the PSRR (use the graph vs. frequency, not the headline numbers) to see how much noise your power supply can generate. If the acceptable power noise level is greater than or comparable to the switcher's output ripple and switching noise, then you can use the SMPS.

If you need less noise, look at using linear regulators: my favorites are the TI TPS7A4900 and TPS7A3000 series, because they provide a lot of PSRR (50 dB or so) out to hundreds of kHz. Then see what the acceptable noise level on their input is, and if the SMPS is less than that. Switching noise (the spikes at the corners of the ripple voltage) can be dealt with by inserting ferrite beads in series with the current before each filter capacitor (not in series with the capacitor itself).