Few things Ford :
First, you're not using Shapechange for shapechange, you're using it for 3.0 haste. As a 9th lvl spell available to most high lvl casters, I don't see that as being all that broken. Mutually assured destruction applies here (Monkey see, Monkey do).
Secondly, while chokers do seem to have the ability to manipulate components, it's a DM's call as to whether or not their 'hands' (or, as the MM refers to them, 'tentacles with multiple knobby joints of cartilage) are capable of performing the somatic's required of some spellcasting.
Thirdly, IIRC, All gear worn/items carried are merged into your form when you change shape and become nonfunctional, so in order to cast any of the spells which require a focus and/or material components, you'd have to set said components down on the ground, change shape, and then pick them up (Or have some other way of not holding them when you change shape).
Finally, b/c all gear is removed, you loose any enhancements/protections/buffs from said gear. While this doesn't apply so much to us right now as we don't HAVE any gear, it DOES still matter.