I agree, Exeter is a total nightmare in summer months. It’s also the only “proper” MSA for anyone travelling between West Hampshire/Dorset and Cornwall.It can be pretty horrific in summer due to capacity issues in the building, and as it’s off the motorway in an industrial estate so you can get badly stuck in traffic getting in and out which is pretty annoying. As I understand it Devon County Council (and/or others) plan to close both Exeter and Collumpton and build a new set of services directly off the motorway in between. It sounds pretty sensible as it would enable better facilities all round and it would keep the motorway traffic away from the local roads.
Closing Exeter would seem sensible from a traffic management point of view and free up valuable land for development, although relocating the MSA to north of J29 would mean the loss of facilities for traffic coming from Honiton on the A30.