There's another reason I'd renew beforehand:
I've always found their policy of choosing to either carry two passports or pay to have the visa transferred struck me as very sensible. Now, I don't know if this regulation comes from them, or they are bound by some outside third-agency rules, but if it comes from them, I'd always wonder if/when they were gonna change the regulation and make visa transfer a requirement.
Paranoia, you know?