The plane came with both. To be honest, I like it. You need two radios/nav units anyway...might as well make them smarter nav/com's.
I usually have the 530 on the map (Nav page 2) and the 430 on nav page 1. Having multiple allows you to display different things simultaneously (traffic, terrain, wx, maps, flt plan, etc). Is it required, no. Necessary, no. To each their own. I do agree that if all you had was the money to do one thing and it was between a second GPS and a PFD, I'd go with the PFD. I have an install appointment in the next month to get the G5 installed. With my 530,430,340,327,gmx200, and G5 I will be having Garmin overload! I'd love a G500/600 but given current equipment and price it's just not in the cards right now. I'm going to give it a couple years and see where we are with previously experimental STC'ed electronics before I do the complete panel makeover.