Depends on what game calls an achievement .. for example, in Saga of Ryzom provides achievements for:
1. Gear
Equipping a set of +Health Jewels of level 50, 100, 150, 200 and 250 ... at 250that adds 1250 HP to my toon
Again for + Sap (magic power)
Again for + Stamina (aka melee power)
Again for + Focus (aka harvesting power)
Then all of the above for armor
Then all of the above for weapons
2. Exploring
Visit all the important places in one of the lakes subregion
Again for the other 6 subregions in lakes
All of the above for the other 5 major regions
All of the outposts in the 6 regions
3. Skills
Reach level 20, 50, 100, 150, 200 and 250 in a skill
Reach Level 230 in 5, 10, 15, 20 ... 60, all 63 skills
On the way, there's achievements broken down in 4 categories (melee, magic, craft and harvest
4. Fame
Reach maximum fame level with various factions and factions
5. Occupations
Reaching various levels in 8 occupations
6. Heroic Deeds
various rewards for completing a complete set of the above
The thing is , you are going to want to do almost all of these this anyway. Would you ever say ....
- Nah not worth my time to get level 250 armor / weapons
- Nah I'm not interested in exploring that region
- Maybe you might say ... Oh I just wanna be a tank ... why ? Leveling magic makes you a better tank because now you have better resistance to being attacked and killed by magic. Not harvesting, means crap gear
-Fame is useless at 1st glance except that my raising your fame with tribes, factions .. they pay you more ... they charge you less. If your fame is above a certain level, then when being chased by a bunch of whatever, if you get in range of them, thy will help defend you against whatever ... if it is below a certain level, if ya get w/i range they kill you ... so you are gonna want to be at the minimum
-Occupations... yeah they give nice rewards and the highest level once are the best so ya gonna do them too
So achievements that have a monetray cost, want nothing to do with that. But almost all of the above provide worthwhile IG rewards and the achievement is like "getting the gold star" in elementary school. As for the fame, getting the trigger points where you go from getting KoS'd to getting aid are significant. Getting better pay for missions is helpful but really don't care for "better prices" as anything they selling I can make better .... But I'll take on a few extra missions on to get to max fame ... to get that gold star so to speak. It's a nice break from routine and doesn't involve a lot of effort.
I should note that the game's been around 15 years and average player age is > 35. And yes, there are a number of folks playing since the get go who "haven't finished yet"