CycleToWork upgrade?

[kingabunyip]

Hi guys

First post

I currently have a Planet X Maratona with Vision Comp 35 wheels and full Ultegra groupset. I got the bike last year on the cycle to work scheme.

The year is almost up so I can get another £1000 voucher through work.

I'd like to upgrade, so can I get some advice/opinions on what would be the best bang for my buck.

The 3 things I'm thinking are:
1. A new frame
2. New wheels
3. Di2

Thanks in advance