Jewish homeland in Western Sahara ? It would take forceful relocation. W. Sahara is by far lousiest of all alternatives available to European Jews for the nation-building project (and Mizrahi were not that interested in the project at this point). In addition to "Uganda" (it was really a territory of OTL Kenia which had been offered, not Uganda), Australia, Palestine and Birobidzhan being mentioned here, there was Argentine. So, chances of Jews coming to W.S. at their own will is less than zero. So you need some TL with Hitler going Mediterranean instead of Barbarossa and deciding thet dumping Jews in the desert is not bad idea at all.
Also, Morocco was not very jewish friendly just after the independence, so if the jewish state is create in a territory they consider theirs, we could have a similar problem than in OTL.
Morocco is actually one of more philosemitic Arab countries (not that it does say a lot). Anyway, I doubt that Moroccan army is powerful enough to express it displeasure in terms of force in mid-1970s if Jewish W. Sahara came into being in 1940s.
Birobidzhan didn't go that hot, and Birobidzhan's not really too bad at all in comparison. Granted, there was a Stalin to deal with there as well, but even Soviet Jews largely stayed away.
Birobidzhan came into being at rather unfortunate point in history, as far as Jewish asgricultural settlement programs go. All attempts (including OTL Israel) are directly linked to creating a refuge in the time of hardships, and the biggest waves of settlers naturally come from areas with the strongest oppression. However, 1925-1940 was the gold age of Soviet Jewry as far as their place within the society is concerned. They were subjected to same Stalin's antics as anyone else, but Antisemitism was largely absent as coherent policy. And, given a choice between coming to industrial centers and going to chop trees in the Taiga, Soviet Jewry made an obvious choice.
aside from the historical meaning, what's prime about Palestine?
Nothing, really. But the whole project had been driven by idealism, not economical considerations (ones who were driven by economy went to North America).