what is wrong with an aluminum Lightweight Back-Plates and travel wing? . . . The OP was looking for a travel bc, so saving 6# using an al backplate and smaller wing for travel is much cheaper than buying a new "travel only" bc. Also the 6# is cheaper than the $25 per trip for airline weight allowance when using the steel plate. A al plate can be found for under a under $100 and will last for years/
There is nothing 'wrong' with an AL plate. I have one. For that matter, there is also nothing wrong with the lighter weight (2lb) SS plates. Or, one of the 'soft' backplates (e.g. the Apeks Travel Plate). There may be consequences, in terms of weight distribution.
What the OP actually asked for is 'advice?'. So, my 'advice' is to travel with what he already has, particularly if that rig already works for him, and
not spend money on a different BCD, be it a 'travel' BCD or a lighter plate,
just for travel. Because that is unnecessary. I don't spend more money on bags when I travel, because I have optimized the distribution of weight, between my carry-ons and my checked bags. If the OP wants to spend money, he already has indicated that he may opt for a slightly smaller, more streamlined wing for routine use (which would presumably serve him well for travel as well). Good for him. I readily acknowledge that it is his money and he can ultimately spend it anyway he chooses. My 'advice' would be to spend it on the newer, smaller, streamlined wing.
I personally benefit from the weight of a SS BP, to help avoid strapping on additional lead - again, all of this is personal preference, and the OP's bioprene quotient may be different than mine.
If I use an AL plate, or a soft plate, with a single cylinder, I end up strapping 4 lbs of lead on my waist, which is below my center of lift, and I end up with trim issues as a consequence of using a lighter plate. Yes, I could put trim pockets on my upper cylinder band, and put 4 lbs of weigh in there. But, that moves the weight away from my body and subtly influences my longitudinal axis stability. Why do either? The SS BP puts that weight where I want it - immediately adjacent to, and spread across, my physiologic center of lift. And, that is true whether I am diving locally, or whether I dive when I travel. The principles of physics and physiology are the same. I do find an AL plate to be very useful - for diving double steels.
I am not suggesting that my 'advice' is somehow better. And, none of this may apply to the OP. But, since he already uses a SS plate, quite possibly it does. Why change what is already working, if you don't need to? Just my 'advice'.