Taking Gaza would be useful, especially if the population flees, but I think that would need the local Arab population from Gaza to make an attack first. Although it wasn't part of Israel at Partition and fighting in a built-up area - not a great idea? Perhaps the Israelis would take it, (or reduce it in size), but I really think they'd need to be provoked first. Pushing the northern GazaStrip border south, say, 5km down from the OTL border looks sensible, as it mostly puts Zikim, Carmia and Yad Mordechai pretty much out of mortar range. Having said all that, the Israelis have bigger fish to fry further north.
There'd certainly be a much smaller West Bank (and as a result no "wasp waist"). Of course one of the big priorities would be to take all of Jerusalem or at least get the Wailing Wall area, beyond what was held OTL. With no Egyptians, maybe they can push the Arab Legion all the way back into Jordan?
Taking all of Galilee is good, given the fertile land up there.
With no Egyptian involvement, taking all the Negev would be easy, there's very little down there, especially in '48.
Might the Israelis even push a little way up onto the Golan, say to a point at which the kibbutzim lower down aren't such easy targets for bored Syrian gunners in future? But there again, that's not part of Partition Palestine, so maybe not.
I think the Royal Egyptian Air Force was the biggest of the combatants air arms, so take that out of the picture and the infant Heyl Ha-Avir probably gets air superiority, especially when the S-199s and Spitfires arrive.
Goodness only knows what the refugee issue would look like, certainly bigger than OTL.