Babuska is right, if you book as a guarantee you are more likely to be upgraded. This is merely part of the nature of a guarantee. The defining characteristic of a guarantee booking is that the cruise line has the ability to move you about at will. They can put you where ever they have an empty slot. So it's not so much that it is an upgrade, as just that they found it convenient to stick you there. That is why they sell guarantees cheaper, it is easier for them..
Aside from that, Upgrades of any consequence are not all that common. By that I mean, almost all upgrades remain within the same class of cabin type. ie: they are inside to inside, or outside to outside, etc. I'm not saying inside to outside is impossible having experienced that once myself. But it is rare.
So even if you are upgraded by the cruise line, the move you get will almost certainly be from one inside cabin to another inside cabin.
Take a look at the deck plans for your ship. I don't know which ship you are on, but suppose it's the Triumph. On that ship there are two more catagories of inside cabin higher than your 4E. If you were upgraded it's likely to merely be to a 4F or 4G. You'd still be in an inside cabin. And trust me, the view from the interior of an inside cabin on the ninth deck is exactly the same as from the interior of an inside cabin on deck two. Such an upgrade is no great thrill, and hardly worth considering an upgrade.
And if you are still hoping the cruise line will upgrade you, remember this, the cruise line is far more inclined to offer those nice upgrades to their many-times-over-past-passengers.
If you really have your heart set on a better cabin, then you really ought to just pay for it.