AD18 does have support for multi-board projects, including validation between boards. I haven't played with it yet, but it does look pretty neat. Activeroute looks slick, but the demos don't show you the prep work in setting up design rules and constraints, so I don't know if it's anywhere near as useful as they make it look.
AD18 was frankly a bit of a disappointment, but mainly because everyone I think got their hopes up about how much of an improvement it was supposed to be. It is definitely a step forward, but not as far as was hoped and there were also a few things that took a step back. However, there has been more activity on Bugcrunch recently, so maybe getting AD18 into the world has allowed them to work on their backlog. I would probably wait until AD19 to see what that brings.
When we were up for renewal this past summer I told our account rep outright that the subscription just plain wasn't worth the sticker price, and if we weren't going to pay that much to renew. To their credit, they gave me a price I was willing to renew at. If you've got five seats that are five years past renewal to dangle in front of them, you can probably work a pretty good deal.