Nah man, I've been in groups where the middle was hardly touched, and we still steamrolled through the opposition. Holding bases is more important. If you can get four bases and hold them for even a minute or so, you'll likely end up with a lead that'll be hard to overcome.
The middle is basically a chance at bonus points. If you can utterly dominate those bonus points, while holding 2-3 bases consistently, you stand a good chance at winning. However you're more likely to either duke it out in the middle for bonus points, splitting the bonus, or the other teams will have put their efforts into capturing bases, in which case having one less alliance to reinforce things will make holding 2-3 bases consistently rather difficult. It's better to secure your bases, and only spare an alliance when Nodes and such are about to pop, assuming an alliance can be spared in the first place.