Is this a practical minimalist 5 V-to-3.3 V circuit?
Yes. Though, depending on how stable the USB 5&nbsp;V source is, and its capacitor/filter on the source side, you may not even need the input capacitor. 

And some 3.3&nbsp;V regulators do not need an output capacitor either under most situations, but the LP2950 does (minimum 2.2&nbsp;µF, with an ESR of 5&nbsp;Ω). 

Additionally, for a truly minimal 5&nbsp;V to 3.3&nbsp;V circuit, you could go with an SMD IC.

For example, the LDCL015XX33 is a capacitor-less SMD (SOT23-5) 3.3&nbsp;V regulator with a 150&nbsp;mA output current.