Pitch from prior yeast cake AND a new vial

I've got a summer weiss set for bottling this weekend. I'm strongly considering doing the exact same recipe again in the same fermenter. Did this brew two summers ago with some friends and it was a huge hit, so i'd like to have a good stash for when the warm weather rolls around.

With this in mind, I recently read about reusing the yeast from your previous batch. Opinions vary about dropping the wort right onto the old yeast cake or harvesting some from the slurry. I'm thinking of doing neither. Instead, I'm thinking I'll just skim some from the top of the yeast cake, maybe 1/3 of a cup, and also pitch a new vial. (Alas, I've not yet gotten into the good habit of making a starter.)

Ambient temps were usually between 66-68 on the first batch's fermentation, which means ferment temps were higher. Not sure if high enough to stress the old yeast, but I'm assuming it can't hurt to pitch a new vial, too, just in case.

Anything about this make it something to avoid?

To me, this would combine the worst of all possible options: the work of harvesting, the contamination risk of multiple yeast sources, the genetic drift of partial skimming, the expense of a new vial, and low viability of a starterless pitch. Why not just pick one approach and do it properly? Get an apple juice jug to make a starter, harvest and wash your yeast, or buy two vials.