Sorry but I really think that none of those services will receive anything new this year, cascaded or otherwise. The 3 doesn't need it, its current fleet (well the majority of it) is only four years old, and fine for the job. I don't think it would be seen as a priority. As for the 4, whilst I agree that the darts are getting on a bit, they are, in my opinion, perfectly suitable for the job and most perform well. The only thing which might tempt First to invest in new buses for the 4 is the recent introduction of the 14 from Wessex, but otherwise the darts are fine. And the 5 won't either. I believe it had a very slight upgrade recently when the 54/05/55 reg B7RLEs took over, though I understand the older 02 reg B7s still appear fairly often so that at least be addressed. There may well be a business case for newer stock on the 5 (as has been hinted at several times over the last couple of years) but I think the current arrangement will stay in place a while longer, with perhaps a few tweeks.
However, whilst I do not anticipate new stock on either service, I do think that unlike other depots, they will invest in the current fleet this year. That is to say I think most the buses will be painted, refurbished inside and route branding applied, so they will look a lot better.