Pointless because you don't need to do them for cash - the cash you gain in the game is essentially useless, as you'll always find enough weapons out there in the galaxy. I don't think I ever bought a single weapon or armor the whole way through. And they're boring because, unlike the story missions, the side missions are generally pretty cookie-cutter. Sometimes the mission itself is okay, but the map is just cut-and-paste of hallway sections and rooms you've seen a zillion times and which you'll see a zillion times again. Apparently people complained about that and the developers took note - the side missions in Mass Effect 2 are pretty damn awesome, to the point that you want to do them all before you bother with the main story mission, despite the fact that THE WHOLE GALAXY is at stake.
So yeah, Skyrim seems very flexible and not repetitive to me. Yeah, some underground places look similar, but hell, underground places are rock and dirt, pretty much the same in one place as another. But at least they do vary visually, more than they did in Oblivion for sure.
I will venture to say that anything will start to feel mind-numbingly dull if you overdo it all at once. Don't spend 40 hours playing the game in one week. It isn't a chore, it isn't work, it isn't something you should feel obliged to grind through and get done. If you get tired at half past midnight, go to bed instead of playing another hour and a half; computer games are not a good outlet for a diehard work ethic.