(08 Jul 2020, 11:24 am)Big O wrote The used bus market offers a chance to pick up similarly sized midi-buses, only a few years old, that may use more in terms of diesel but offer a better quality throughout the life of the contract than the Mellors. The Mellors offer a false economy and are completely knackered after their contract.  Whereas a properly maintained E200 could be used over the span of two or three contracts.  

 Not every route can use midibuses, such as the K2 due to its Sharon Close section, however better planning by Nexus could see the withdrawal and joining of some services together to ensure they are not paying for 2 contacts when they could pay for 1. Sending the 335 to Killingworth replacing the K2 in part is something I think could be beneficial and create a through-link from Quorum to Killingworth and without the need to change at Four Lane Ends.

Which Mellor's are completely knackered by the end of their contract?

https://venturasales.co.uk/sold-vehicles...tucan.html these ones available with Dawsons don't look knackered.
I'd hazard a guess the chassis and engine will be pretty durable being VW Transporter designs and as you say, get around streets something bigger won't. 
The E200's available with Dawsons are dual door. Converting them to meet the spec up here, may suddenly render a route tender unviable.

I agree with what you say in your second point about merging routes. I think they've done that in the past around Washington with the 37/73. However, it will depend on anything attached to the same tender. If there is the need for say two workers services to run off two different routes like the K2 and 335, then it may not be possible to integrate or combine the two.