Hi Charley - I responded to someone asking the same question, also in zone 5 - in the discussions section.

Charley, stay with what has worked for you in the past, if it worked reasonably well.

I have always found that you don't have to wait to see the eyes for next year's harvest. They look like bad pimples, and are fairly obvious up on the collar area of the clump as soon as one digs up the clump.

Saran (or other wrap) has worked well for many, and failed others. The benefit, if it works for you, is the space- saving piling up bundles of tubers offers vs accommodating stacks of tubers clumps in boxes or containers. I'm doing both Gladwrap and vermiculite this winter, after dividing.

I live in Western WA.I have talked to two very experienced dahlia people and they have suggested leaving the dahlias in the ground. After you cut them down, put black plastic material down with 5-10 inches of hay or evergreen fronds on top of the black plastic. Other years I have dug them up, wrapped them in Saran Wrap or put them in vermiculate. Neither has guaranteed eyes or survival. I belong to a Dahlia Society and everyone has tried every way possible to get them through the winter. Leaving them in the ground seems a lot easier.

It very much depends on where the dahlias are growing. In our cold and wet little micro climate, I'd never get away with leaving them in the ground regardless of how much plastic or mulch I used. Gardeners in the warmer, dryer Seattle area or the 'banana belt' on the peninsula can do that, but the dahlia that survives a typical winter in our ground is rare.
It IS much easier to leave them in the ground, but if you want some tubers next spring, rather than piles of mush below ground, you have to dig in cooler zones.