So far, I've managed to get the fossil pet, the gnome pet, and the fossil mount (yay!), as well as a couple other rares that are just flavor pieces (like the dancing dwarves, or the mirror image). Yes, I have been spending a fair amount of time on archaeology (LOL).
I'm at 525, so now I'm just chasing new finds. The problem becomes that it's harder to get the new finds. One example...on Kalimdor, it's hard to get the Tol'vir dig sites because the spawns compete with all the Night Elf, fossil, and other spawns covering the rest of the continent. Also, Dwarf seems to be a little harder to get on Eastern Kingdomes, where Troll sites abound. Night Elf sites are also common in higher levels areas, so Nelf and Troll tend to be overkill. I foresee having to go through a lot of Nelf and Troll sites to ultimately do all the cultures.
As for scrolls, tablets, etc...I don't inherently see any reason to hold onto them. Whether you use them to get 12 pts for a common, or 12 pts for a rare, you still need those 12 pts. Maybe there's a psychological reason for saving them for big projects, but I don't really think it makes a difference. You'll have to get the pts one way or the other anyway.
Overall, I'm addicted to archaeology so far. I may get tired of running all over the place to dig stuff, but for now I just can't stay away.