if the cars straight no need to scrap it, unless youre not prepared to carry out a lot of welding and fabrication work. there will be a lot of work required anyway to seam weld the bay, so you could just plate over the cracks while youre at it, as long as the plate used is thick enough, bent/shaped and welded properly cant see why this wouldnt be ok.

the bulkhead, inner wings and other parts were rotten on my mk3 rs1600i, didnt realise this when i bought it, but after lots of hard work the engine bay is now finished and seam welded, pics etc are in my resto thread, click my sig to have a look/read.