It's probably closer to something along the lines of Coal or Uranium as a power source:
Technically not renewable, but has as much as is needed for most playthroughs. The only time to be really concerned would be either when you're doing an extended playthrough (with the releases of mods and vanilla updates, changes which require entire new maps are relatively common), or if you are wanting to REALLY whore the resources for some obscure reason (like powering a continent-sized MFFS security station purely from vis).
well i am running a erver and had noticed that the vis around spawn was quite low.
On another note, how would you power something like that from vis?