It is important to caramelize the pastry: for flavour, of courxe, but mostly because the caramel forms a sealing layer which protects the pastry from the moist filling (usually cream) and keeps it crisp longer.
If you prefer not to caramelize the pastry, you can glaze
it with egg to make it look more attractive.
Making a successful feuilletage is not easy, especially at first. It is worth remembering that the great French chef Joël Robuchon, when asked: "When was the first time you felt like a real cook?", replied: "The day I made my first successful strawberry millefeuille". So, be brave and have a go!
Actually this not really a good option, with syrup you add some water, which is the enemy of golden crust.
Dusting sugar is the better option for me.
A question: at stage 3, would it work to brush the pastry with sugar syrup (or even just sugar in water) instead of dusting it?