I might be a bore but I'd rather see investment on routes which are busy all year round rather than one 3 month a year, especially when the buses on there are fine as they are and none of the below need old Enviros bar maybe the X46.

X26/X27 - 15 year old Omnicities
X66 / X67 - 15 year old Omnicities
X46 - Ex London ALX400
306 - Whatever Jesmond fancy on the day
1/2/57/57A/58 - 14/15 year old MPD's
685 - 13 year old Omnicities