I don’t think that I can suggest more than what I’ve already said in my “Attic
” category posts. If you know exactly which part of the attic / roof the ice dams are attracted to, start from this particular section of the attic.
Drip edge vent is the last resort if there are no soffit vents installed (or no way to install soffit vents) and it is not necessary if your soffit vents are performing properly and providing sufficient amount of air flow. Also, when covered with snow or even little ice, drip edge vent performance may suffer.
I would rather make sure that there’s nothing blocking the existing soffit vent and that what you see on exterior (screens, grills, etc.) is not just for aesthetic reasons; make sure that there is a cutout along the entire length of the soffit vent.
Furthermore, calculate the air flow area of top and bottom attic / roof vents (50% for each would be ideal) and compare with the square footage of your attic – more is better, especially in cold climates like yours - attic ventilation
One problem with passive roof vents, including the ridge vent, is that they don’t perform well or at all under the snow. Obviously, you’re not going to climb up the roof and remove snow from its ridge. The solution would be to install humidistat controlled power vent which will kick in as soon as the humidity level rises and activates its sensor.
With the soffit / ridge vent configuration you should not have any active gable vents because they disturb air flow between the soffit and the ridge.
Removing the insulation to spray all cracks and openings is a very good idea. You can watch this short video for possible areas to investigate. You could also ensure that there’s a proper vapor retarder installed beneath the insulation.
New England is in a climate zone #6 which requires either a Class I or II vapor retarder on the interior side of frame ceiling (i.e., ceiling drywall – vapor retarder – attic insulation), all the vapor retarder type details can be found here - NAIMA
I hope that helps a little, let me know.