Although the Anschluss was definitely a diplomatic coup for Hitler and a prestige boost, does it really materially affect his preparations for war? I've never read anything to suggest that Austria provided an indispensable source of manpower or industrial capacity for Germany's war effort. Between Hitler and Stalin, Poland will still fall without Austria's participation. Without the Anschluss Czechoslovakia likely remains free, so France and Britain have less warning of Hitler's true ambitions before he makes his move, resulting in lower military readiness.