The current generation of A4 (which yours would be) was updated a couple of years ago, but it wasn't a very significant one. You might not find it feels like a substantial enough upgrade over your current car. We'd either suggest waiting for the next-gen A4 to come out (expect that to be revealed later this year) and for used models to appear in your budget, or consider looking at the latest BMW 3 Series or Mercedes C-Class. Both of those cars are a generation ahead of the A4 and feel it.