Transit LAN vs. Individual LANs

I have 2 core routers (CR) and 3 access routers (AR) currently connected point-to-point where each AR connects to each CR for a total of 6 ckts. Now someone has decided to connect them with Gig-E. I was wondering about the benefits or disadvantages of keeping the ckts each in their own individual LANs or tying them all into one VLAN for a "Transit LAN" as those folks that decided on going to Gig-E aren't doing any logical network architecting (is that a real word?). Anyone got any suggestions, comments or helpful hints? Thanks, scott