I don't think any gameboy game could beat a console on length, unless you got really hung up on a puzzle and just couldn't get past it no matter how much time you spent beating your head against it.
I didn't play much of FFX, but most of the time that I did spend on it was playing Blitzball. I for one found it to be quite enjoyable, if seemingly fruitless in the short run. I have heard that someone has filled up everyone's sphere grids to the max, which is absolutely insane. But four days... All I can think of to say to that is get some friends. Or some sun. Preferably both.
I for one don't usually bother with all of the sidequests. I do what interests me, and the ones that I actually find and aren't overly tedious. Breeding a gold chocobo in FF7? Not happening at all. I got one, but I took a shortcut through the Weapons, which I'm sure is much faster. The tedium of some sidequests just detracts from my enjoying the game.