Seems like a decent solution.
Do you run cold? Reason why I ask, is because for myself, that would be overkill for 55*F. At home, I sleep completely au naturale under a thin, very breathable sheet at temps between 65 to 67, and I’m completely fine. That’s with no wind obviously. If I wore a light insulated jacket (or a baselayer+mid layer+wind jacket), pants, warm socks, etc and used an UL bivy that blocks wind well (perhaps also heat reflecting one like the SOL Escape bivy), I would be completely fine at 55*F and probably could push it down to around 50. And I assume that most of the above, minus the bivy, would be things you would be bringing anyways, so no extra weight and expense.
On a side note, for cheaper alternatives to Alpha Direct. Alpha Direct is not some kind of super specialized material. It is basically just fuzzy/slightly furry polyester fabric that is breathable. If people are looking to save money, going down to Joanne Fabrics or the like, and looking at their lightest, synthetic faux fur type fabrics will get you similar insulation per weight wise at much less cost (especially if you use a coupon like I usually do).
Another inexpensive alternative is taking a couple layers of some of that really light weight non woven polypropylene material and sewing it within a stronger, woven, more wind resistant UL nylon fabric (like Argon 49) to increase durability. Keep in mind that polypropylene is 35% lighter than polyester while also being less thermally conductive. And the above stuff is dirt cheap, like literally. The downside of the non woven, light stuff is that it is kind of fragile, but that is why you would sew it within a matrix of the woven nylon, and double over the seam areas of the PP material (so if you have two layers, folding it over and sewing would give you four layers, not including the more robust nylon).
Also, it would be extremely water resistant and would dry significantly faster than even Alpha Direct. PP has a low enough surface energy that it has a built in, natural DWR so to speak. As long as it doesn’t get really dirty (the nylon cover would help with this), it will always repel water and doesn’t absorb any into the material itself (just in the in between spaces of the material).
Some years back, there was a discussion about Milo’s bivies made out of a (more robust) polypropylene non woven fabric. People who had used them, commented on how surprisingly warm they were. Richard Nisley got involved and pointed to a combo of the low density of the material with low CFM combined with a thermally resistant material (lower conductivity than every other fabric material) made for a warm for the weight material. (Incidentally, 35% polypropylene/olefin fibers are the “secret sauce” to thinsulate insulation).
Anyways, if you’re looking to save weight and cost, then that latter, 2nd solution would be your best bet, while also being extremely water resistant and extremely quick drying. But for self, since I run apparently warmer than the average, I would just wear clothes and with my SOL Escape bivy, I would be fine for those temps.