It's not that I'd expect the school to accept the WISC and not the WPPSI, but I know that some school districts, ours included, won't take scores that are more than a few years old. In some places it is one year, in others three. Having recent testing that supports the earlier testing might be beneficial, but I wouldn't fork out the $ until I was sure they'd use it.

Study Strategies for Accelerated Learners