STO is a great game now and I myself put tons of time and effort into it.
I think what your looking at is pretty much the advantage of a properly supported and run endgame, as opposed to MMOS that are generally unable to provide much to do once you get through the basic character advancement process, and release new content very, very, slowly with rarely even so much as a reliable hint about anything new being on the way. STO has done a pretty good job since it's 11th hour FTP recovery of releasing new content at a reasonable pace and providing something for established players to keep working towards... which sounds simple, but is where a lot of MMOs wind up failing. Most MMOs seem to think they can launch without much thought into the endgame and worry about adding it in later, and that just generally does not work, even for FTP titles. One of the big concerns about the upcoming "next gen" MMORPGS like "Wildstar" and "Elder Scrolls Online" is that they want to bring back the subscription model, but have largely remained close lipped about how they plan to run an endgame and produce content fast enough in order to justify that model when even a lot of FTP games can't pull it off, and as more and more games like STO demonstrate how it's done, the bar is constantly rising, especially if you want to even consider membership fees.
As far as the central issue of MMO "addiction" for all the people who call themselves addicts there really isn't such a thing. In cases where there might seem to be an actual addiction at play it's more a matter of the person being unstable to begin with, rather than a true addiction. The thing about MMOs is that the term "game" which is attached to them doesn't really fit, MMOs tend to be more of a hobby, which is something that a lot of people don't realize when they get into them, or have trouble understanding when looking at them from the outside, especially when the term "Game" keeps being thrown around. It's more akin to making model boats or something than it is to playing a game, as in general it's something that is ongoing and keeps being built on as you play it, with the people involved generally staying involved due to their accomplishments and watching the game and it's community develop. Given that it's all digital and there is no physical, real world, product of the effort, it can be difficult to understand, but at the same time as the concept of digital property is becoming increasingly understood I suspect that will change. What's more I've honestly contemplated as to whether the lack of any kind of physical prescence of this hobby despite it's expense is really a diaadvantage having seen the clutter and mess caused by people pursueing hobbies like model building, shoe making,
and similar things in their spare time. Though I do admit gaming doesn't actually have any practical benefits other than entertainment, it's hardly the only hobby that this can be claimed of.
As far as how much effort and life adjustment goes into it, while it doesn't have the same amount of mainstream acceptance, compare playing an MMO or a PNP RPG to one of the more involved fantasy football leagues people get involved in. You can see people spending hundreds of hours and tons of money on things like long distance phone calls trying to work scores, make trades with other players who could be anywhere in the world depending on the size of league and it's scope, and other things, just for the bragging rights of where they placed in comparison to other pretend managers in predicting how things were going to turn out for the year. At the end of the day it's all about how much fun you had doing it, which is the point of most hobbies like this.