X13: Commuters to/from Newcastle do use the 43 to beyond Cramlington, so, backwards step withdrawing this link. X13 would also provide an unneeded link between Blyth and Cramlington, like we haven't got enough already.
X14: Like mb134 said above, this would have a negative impact on the A1 express corridor.
X17: Great idea, but doesn't need to be X-prefixed as it isn't an 'inter-urban model' service. See below for my thoughts on terminating at Amble. Also, serving/terminating at Alnmouth Village may be beneficial, however, this may impede on X20 calling at the Station, and X18 calling at the Village if not timetabled carefully.
X19: Just seems to be a pointless route? Can't see any real demand for a further route from Blyth down the coast.
X20: It's a well used route from South East Northumberland to Alnwick. The Max upgrade and Alnwick extension caused a massive increase in overall passengers using the service. Withdrawing the Amble-Alnwick section will be a very backwards step.
RE: Arriva North East: Service Suggestions