Ibanez R400 Ragtime - warped neck repair


I have had this lovely Ibanez acoustic model (with cutaway) since I purchased it new back in 1981. In the past couple of years, it has developed some noticeable dead-spots around the 4th to eighth frets which my local guitar shop have attributed to a convex warp of the neck/fretboard as well as a twist  from one end of the fretboard to the other. To fix the problem, they tell me it will be necessary to remove the fretboard, correct the bow and twist problem then re-glue the fretboard, making good any damage to the lacquer caused by steaming off the fretboard.. They say that the warp is beyond that which could be corrected with the truss-rod.

This work is estimated to cost about £200 and looking at the guitar's value online, it is not much more than that as a second hand instrument,. which raises the question as to what I could get for the same money put toward a new or used guitar. Thing is, I am very fond of my Ibanez except that in it's current condition it has lost its sustain and tone and sounds...dead. How likely is it that the luthier's repairs will restore the original tone? Is it worth my trying to heat the neck and correct the twist myself ( without removing the fretboard) ? Or should I say goodbye to it and look for another acoustic? 

Any comments or suggestions would be appreciated.,