Yeah, VCAs are super-duper important! In addition to controlling audio levels, you also use them for controlling modulation levels. Want a slowly-widening sinewave sweeper to modulate a VCO? You'll need a VCA after your mod source, and an EG to do the rise/fall of the waveform level, then send the result on to your VCO(s). You can also feed an audio signal into both the control and signal inputs and use a VCA as a very effective AM modulator. Or you can rig two up to work as an autopanner. And so on. Very much a bread-n-butter device.
As for the 2hp effects...if you're OK with not tweaking the controls on that module all the time, then sure. But something fitting into 2 hp of space doesn't lend itself to constant user manipulation. Keep that in mind...