Reflecting on the result overnight it does seem to me that there is a pragmatic solution going forward, if AEPG wants to engage. (and of course, I don't know what the deal is between AEPG and the Agricultural Society)
As things stand, AEPG can't get 650 houses built on the land that includes the stadium. I don't know what the profit margin per house is but let's assume that is a net potential loss of circa £50m.
AEPG could offer to replace the proposed golf driving range at the southern end of the site, which as far as I can see is adjacent to commercial buildings and as far away as possible from its new build housing, with a replacement speedway track and associated buildings, with the proviso that the Council then approves the majority of the remaining new housing.
That gives a solution whereby, albeit with a bit of compromise, all parties can claim a win.
Of course, they could just bide their time and hope that eventually they get what they want.