I've been playing for almost 30 years. My first good guitar was a Les Paul Custom, bought new in 1980 and still with me today (looks like my avatar). Throughout the 80s and early 90s, I was content to switch off between the LP and a Kramer, or Ibanez, or some other super-Strat flavor of the month instrument.
In the late 90s, I started to really analyze guitar sounds, especially since I was getting into blues, country, roots rock, and other things besides heavy metal. I started to learn how different guitars have innate sonic qualities, and where the strengths, weaknesses and uses for those qualities are. In short, I think a well-rounded sonic assortment for a guitarist would be a collection containing:
A dual humbucker solid body with a fixed bridge (Les Paul, SG, Explorer, McCarty)
A P90 pickup solid body (Les Paul Junior, Special)
A Strat type with three single coil pickups and vibrato bar
A Tele type with barrel saddled bridge
Something jangly, maybe even a 12 string electric (Dano, Rick)
A super-Strat, with humbuckers (at least one) and a Floyd type bridge
A hollow body arch top that benefits from a wound third string
Acoustics, steel and nylon string, 12 string
A bass
A baritone or seven string (although personally I would not use one)
What am I missing?