On the subject of collection values, I did quite a lot of testing before the DecaDynasty and have done a more little since then, although someone will have to help out with items from other EPs.
Definitely valuable enough
Photos: several thousand easily.
Gems: tiberium §30-40K. Rainbow gems and pink diamonds a few thousand.
Inventions: masterful time machines are §2024 each. I’ve forgotten what normal ones are worth but think they’re still >§1000
Paintings: several thousand.
Sculptures: probably even better
Career rewards: OK for private eyes. Maybe combine other careers? (Good luck, on this timespan!)
LTHP rewards. (Are these allowed?)
Iffy
Deathfish in bowls: worth about §1-2K (less than in inventory, for some reason). An expert angler who really concentrated on deathfish might do better but it seems unlikely with the time restrictions in this dynasty. Mounting them knocks the values down to §200 or so. Edit: fish in bowls might be a problem unless they're placed just before moving to a new town!
Skill certificates (Renaissance Sim?): §1000
Gnomes (if allowed) §1000ish
Spirits: §1000-1500
Metals: mummitomium around §1800; titanium §1000+. I think all the others are less but I’m not sure.
Butterflies: glowy, Cleopatra and rainbow all worth §1000+ but hard to find
Beetles: assassins around §800, rainbows (if you can find them!) §1000+. With UL and plasma bugs, this moves into the ‘definitely OK’ category.
Space rocks: gigantic are §3000+ and could be worth a lot more when analysed – but unlikely without help from dogs, werewolves or aliens. Someone with both challenges complete might be OK with smaller ones. (I think my Immortal Dynasty founder was my last Awesomest Rock Collector, so this could well have changed in the meantime.)
Nectar: high quality nectar when aged would definitely qualify but time’s short here.
Books: aren’t worth as much as you’d think, given the royalties. Even masterpieces tend to be less than §1000.
Criminal career objects: possibly OK (if allowed) but getting through such a buggy career on medium might be tricky.
Relics: certainly valuable enough but travelling time is limited.
Stolen items. (Again, are these allowed?)
Wedding presents (ditto) – depends on luck.
Only OK combined with something more expensive
Fireflies(?) My Sims haven’t caught the very rare ones, so this could easily be wrong
Wildflowers – a few hundred.
All types of small pets: up to a few hundred
Plants are worthless. Money bags up to about §800. I think I’ve seen someone say that one of the coffee beans is worth a similar amount. Books grown on omniplants can be worth a lot more, if they count.
Potions: worthless.