Although I do use an Al plate when traveling, the reality is a steel plate does not add that much to your suitcase often you can save weight in other areas. In warm water a steel plate is great because it offsets the buoyancy swing of the common Al tanks you find at most tropical destinations, this combined with a thin wetsuit often means you need very little if any additional weight.
I own a travel set and local set not because I needed it but more because I'm a gear freak with more money than sense.
I do however get your thinking. If I were you, unless you're loaded with cash in which case buy both, I'd buy the plate based on the majority of my diving and a steel plate would probaby suit your local diving needs better. But I'm not you so of course buy the one you want, you won't really go wrong either way and like most divers if you stick with it you will end up with more than one plate/rig anyway.
Good luck, feel free to ask any other questions and rembember most of what people will tell you, including me, is based on personal preference and opinion so have a good read around talk to other more experienced divers if you can get as much info as possible and don't rush into anything, diving is expensive anyway and buying twice is super expensive lol....
