Sort of like a short-term vs long-term investment decision.

Eventually, provided you keep the accounts current by earning once in 3 years and no-one goes bankrupt - you will get the miles up to a redemption level so taking advatage of lucrative bonuses is worth it in my view.

It also helps to have a few mileage options, that way you feel like you are getting somewhere when you pick up a cheap HP flight for a holiday rather than paying $100 more to fly CO or NW because you are trying to concentrate your miles.

However, the bonus has to be significant and worth the time and effort of having low mileage accounts hanging around.