I'd recommend you run some A/B tests. In our experience with site revamps, it's best to ensure your visitors are happy first, whcih you can measure using conversion rates.
If you notice a big dip in conversions, something may be broken which could then have a knock-on effect with your rankings.
From a massive revamp we recently did to make things responsive (1.5M pges) we noticed an increase in most of our rankings.
But just remember - treat google as a mobile user, so if you start simple and progressively add more content via ajax as the screen size increases, remember google may not pick these up, it will see your 'simplest' page, so make sure you don't remove any important on-page factors.