The fin shroud and nosecone are fine for what this rocket is meant to do.
If you don't crash it, the nosecone will hold up just fine for years. It is designed to withstand flight stresses and it is way more than strong enough to do that. I built 6 of these 6 years ago for school demos and except for the one that wintered in a tree they are all still fine after numerous flights. Stiffening the nosecone with CA will make the paper marginally less flexible but flight will not be improved by that. If it lawn darts, the nosecone will still crush even if you stiffen it with CA. So CA'ing the nosecone adds weight but gets you no real advantage.
As for the fin shroud, it is indeed flexible. Once you add the 4 fins, however, they act as stringers and the shroud is much stiffer. Again, it is perfectly adequate for the flight stresses this rocket is meant to encounter. Stiffening or reinforcing the shroud will not make this rocket fly straighter or go higher, nor will it help keep the fins on if the rocket crashes. So, again, adding CA yields no real flight advantage.
I didn't respond to your post to criticize you. I responded because of the numerous responses telling you "how" to do something without mentioning "whether" you needed to do it at all. The Acme Spitfire is brilliantly designed by the most innovative rocket designer currently producing kits. Jim Flis is a genius at producing unique flying machines (foam cup rear-ejection rockets, two and three canted motor kits, ultra easy to build classroom kits, multistage cone rockets, micro-rockets). What Jim truly excels at is building light but strong (as an aside, he also truly excels at being able to convert unique designs into kits others can build, with exceptionally clear building instructions, all of which requires huge talent).
Jim doesn't design rockets to survive lawn darts or being stepped on. But each of his designs is more than strong enough to do what it is supposed to do, which is to fly straight and true and last for lots and lots of flights. I have learned a huge amount from building Jim's designs.
I understand how someone might be concerned in looking at one of his designs that it might have strength issues. But I've yet to find one of his rockets, built the way he tells you to, that actually does have strength issues. The real issue with the Spitfire is whether "stronger" equals "better". I don't think it does.
Steve
