Of course more Doctor Who is always awesome, but first and foremost I would have guaranteed at least some coherency and stability in the series we got. Between 2010 and 2013 we got three series (not necessarily "rather than four" as that is a very demanding sort of attitude, I guess), of which there was a lot right and a lot wrong. One of the biggest criticisms, and it is actually more obvious with the element of hindsight, is that the series gaps did not help.
The Series 6 divide wasn't too bad, but at the same time I don't feel that it benefited in anyway. In fact, you could probably argue that the divide is what led to the structure lending itself to the one-part finale we got, and I wasn't a fan of that.
The Series 7 divide was considerably worse. It wasn't an equal divide (5 episodes in one "half" and eight in the other "half"), and when combined with the standalone nature of the stories offered up that year it meant that the Pond's final run of episodes felt very reminiscent of the 2009 Specials year - and that's no good thing. The latter Clara-half of the series didn't fare much better, feeling like an abbreviated series rather than the second half of one - and that's being generous. When viewed collectively the seventh series feels more coherent - the Oswin appearance in the first half, and the few Amy references in the second half help it it to feel more complete. And so I would argue that while a series every year between 2010 and 2013 would have been brilliant, it was the structuring of the series we got that mattered most and the show was let down a little. Experimenting both with the story type, and the series structure simultaneously didn't do it any favours, so whilst four series rather than three sounds great in theory I'd also exercise caution if it were me and actually try to make the three series we got as stellar a final product as possible.
And it feels important to add that this is by no means a dig at anyone who worked on the show throughout the Smith Era. I loved Smith's Doctor but felt he was having to do his absolute best with minimal to go on some of the time. And I'm sure that the Anniversary was somewhat responsible in no small measure for the scheduling issues with Series 7 - having to fit in a whole extra feature-length special on top of the regular output isn't necessarily easy... and with that in mind perhaps the decision to split Series 6 into the autumn was a bad decision, as it likely held back Series 7 as well.