I asked Paul von McKeown, a friend of mine in Germany who is bilingual in German and English and owns a superb collection of Pickelhauben . Here is his comment, suggesting that I was half-right:
Haube means literally "bonnet" or headdress of some sort, and pickel is "pimple", or can also be "pick" as in 'Eispickel'. But I think everyone would associate this word with 'spike' or 'Spitze'. Spike in German would be 'Spitze', which is the correct term for that part of the helmet, 'Spitzenhals', 'Spitzenteller', 'Kreuzblatt' would be synonym or related to this. Just looking in my French dictionary, (my English dictionary I gave to a friend in Berlin several years ago!) under 'Picke' (Spitzhacke) = pioche; Pickel = piolet, bouton. But of course, in the official army Jargon of the time nobody said "Pickelhaube", not officially, but simply "Helm" or "Lederhelm" to differenciate from the 'Stahlhelm' of the cuirassiers.
Bruno