At level 9, you can upgrade Greater Totem to either Greater Vision Totem (1 pink, permanent) or Greater Stealth Totem (3 x 3 min wards). How should I decide the upgrade path to take, and as a non-support when should I consider paying the 475g for an upgrade?
If you are a non support you have 2 options:
Sweeping lens (most commonly used in higher elos)
You can switch your trinket for a sweeping lens to clear wards. This allows more baron control or you can clear wards to force a enemy to come near a bush so you can kill them. Of course you don't want to use it versus a team comp that has champions who can easily check a bush on high range (Lux/Lucian for example)
If you need permanent map control and/or the cleanse of a normal ward you can use a sight ward. If positioned right a sight ward can grant you vision for a really long time (deathbush for example). I usually take this option on most non supports, since you got a permanent ward on comparatively low cooldown and you can also clear a dragon/baron area. It just allows more utility.
Of course you can also upgrade it to a normal sightward but that isn't that benefitial. Of course it's a good thing if you are still in the laning phase after 30 minutes but generally the rule boot upgrades > trinket upgrade counts. And if you could afford both you can easily buy a chain west/pickaxe/blasting wand situational to the champ you are playing.
You usually want to upgrade your trinket last or if you got 475 gold to spend and you have no problem of farming that gold up again after you leave the base.
As a support both rules count but there are some exeptions
Buy it if you are a support that relies on bush stealth (Blitz/Thresh/Leona) and you can instantly charge/grab an opponent that comes to close.
Buy it after you finish your sightstone so you have 3 normal wards and 1 pink ward almost all the time.