I see on the wiki that certain elite NPC's say things like "share with levels 60-180." Is this just a recommendation, or does this mean people above rank 180 and below 60 cannot attack that NPC? As well, with non-elite NPC's, will I at some point reach a level where I can no longer see for example the level 5 Ravid, lazuli scout? I don't want to keep leveling up if I am going to miss out on some NPC-specific artifacts.

For the first question...your second analysis is correct. To put it better, the alert will only appear to those between ranks 60 and 180.

As to your second, many non-matched NPCs (and some matched, but you don't have to worry about that for a loooong time) will disappear after a certain rank. Many of them will be replaced by NPCs with similar or better rewards (this is what you're concerned about, yes?), for example, Ravid drops Lazuli Parts Vaults...similarly, a number of Lazuli elites also have a chance to drop those, which are only accessible at the higher ranks. Other NPCs, like the Drannik Ballistae, do not have any replacements, but have a fairly large window (I think I read somewhere that Drannik Ballistae stop appearing around rank 600 and possibly start appearing around 120...so that's a pretty big window).

The rank range refers to the ranks that are able to see the NPC once you alert it - so in your case, no one below rank 60 and no one above rank 180 would even see the NPC.

Ravid, Lazuli Scouts do disappear after a certain rank. I remember seeing my last one around rank 26 or so.

edit: to add to the response... Lazuli factory complexes (50- 180), Reynard, Lazuli titans (150 - 600) and Renegar, lazuli stations (125 - 600) also drop parts vaults, though not as frequently

Though something to keep in mind as you are growing is this. While yes they do get replaced by a better higher ranked NPC for a while they do stop coming out with many of the high end NPC's at some rank as well. I no longer get the part vaults at my rank and don't remember the last time I got one. lol Though I do see many NPC's that you will not see for a very long time as well. So it goes back and forth.

use the Wiki learn what rank they stop at. Make sure you get ALL your ship mods before you lose the ablity to see the npc.

This is exactly what I was looking for. Thanks.