I'd say that if you do games just for fun, go for what your heart demands. If you want to make a very big game, just go for it!
The problem I see is if you want to have some success in the store and/or win money from them. There are a lot of new games everyday and if you focus in only one big game I see only 2 posibilities: it becomes a hit (you win a lot of money), or the other one, you have almost no downloads. Yeah, it may be a very good game, but you never know how people will react in a so saturated market.
My point of view, and what I'm trying to achieve: make good games (this is a must, the game has to be good, I mean, addictive, good graphics and no bugs), but I'd put a limit of 3 months per game. If a game is doing well in the store, then update it with more levels, more stuff, maybe IAPs... if a game doesn't have success, just forget it, you may think it's a good game, but if people don't like it... you don't have more options.
And there is another thing. Working alone can make you abandon your own projects if they take too much time...