thats a fair call,
its difficult as its not an insurance job; if it was and it was within the costs i would have had it done, and if you'd lost confidence in the car then sell it on.
but as your having to stump up the cash yourself for all repairs it makes it a hard call.
if it were me, i'd probably repair for as little as i could then sell on after. i did with my old MR2 when i had a new engine put in, after that i didn't feel the same about the car; lost my trust in it. so i sold it on in the end.
you have a big advantage that the car isn't currently graded as a Cat D or Cat C. so nothing will come up on the HPI.