For what it's worth, I think that Justice McIntyre is right in this case. When a plaintiff gets a judgment in another state by default, and thereafter registers this judgment in California, the defendant can assert the absence of personal jurisdiction in the rendering state at any time. They're not bound by the 30-day limit established in CCP 1710.40. At the same time, the contrary argument raised by the (losing) appellant here shouldn't be sanctioned.
The only thing I'd add to Justice McIntyre's analysis is this. Justice McIntyre focuses on the fact that judgments without personal jurisdiction are void. Which is totally true, of course. But that does not mean that sister states can't place their own internal or procedural limits -- if they prefer -- on challenges to such judgments. For example, if CCP 1710.40 said that once a sister state judgment was registered, you had 30 days from notice of that registration to challenge personal jurisdiction in the rendering state, or be forever barred from any such challenge in California, that'd be permissible. California could then enforce the "void" judgment -- moreover, the plaintiff would be affirmatively entitled to do so -- after the expiration of that 30-day period. Sure, the sister state judment wouldn't be entitled to full faith and credit under the Constitution, but California could nonetheless permissibly grant it such effect as a matter of legislative grace. And the Due Process Clause would mean that the sister state judgment wasn't initially valid, but assuming the registration state (here, California) had both jurisdiction and proper notice -- which it seems exists here -- the 30 day rule would be a permissible one, and the judgment of the California court would be constitutionally valid.
Admittedly, in the end, I agree with Justice McIntyre that Section 1710.40 doesn't do that; instead, that it adopts a preferred rather than exclusive means through which to challenge a registered sister state judgment. I'm just saying that, if it were me, I might have relied a little less on the whole "void" stuff. Which is true, but not really what the case turns on. Crazily enough, even void judgments can be enforced sometimes. Just not here.