Let's say it did for me, because I was able to put more of the details it contained into perspective. I would recommend only rereading it after you've gone through the entire series at least once, however (I only picked it up again after having read some of the other books several times) -- AND letting a certain amount of time go by between the last reread of another Wimsey book and going back to "Whose Body?".
Not sure about "needs" -- but it's what worked for me. :) Also, it probably depends on which book from the series is / was your last read before revisiting "Whose Body?". For me, it had been "Gaudy Night" ... and there was no way I was going to reread that one in direct sequence with "Whose Body?", because I was certain it wouldn't leave me free and unbiased enough to even *see* things in "Whose Body?" that I hadn't seen when first reading it.