I started a year ago with an eGo-c, and just like you, was quite satisfied with the vape.
Got into a co-op and lavatube. (now have many more vv devices) and, like you, I am finding that overall, my sweet spot is a 1.8 to 2.0 ohm coil with the Vivi at 3.7 volts!
Thing is, as others are stating, overall it is the wattage that gives the vape/satisfaction. (for me) the juice can also make a difference in where I set things, and even what delivery system is used.
Like I have a vanilla cupcake mix, that tastes bland with a 1.8ohm single coil at 3.7volts. I put it in a DCT at 3.0 ohms, and kick it up to 5 volts, and it's an all day vape for me. YET, a smore flavor, (chocolate) tastes nasty in a 3ohm dual coil. Put that in a 1.8 ohm dual coil, and 4.2 volts, and THAT is now an all day vape.
IMO different juices, can be really brought to life (or death) via variable voltages, and using different ohm's.
If you stick with one flavor, or basic style, then you may be just fine with out vv. BUT if you love experimenting with different flavors, and making more of a fun hobby of this (especially if you get into DIY) the VV is the way to go for sure.
Either way, if YOU are happy with the vape of a 3.7 standard device. STICK with it!!! If it keeps you happy, and off analogs, that is what matters.