I'm a VCAP-DCD in 5.5 and personally speaking it made a huge difference to my career.
Over the course of 4.5 years I've gone from a Break/Fix FSE to being an Architect, part of this process has been travelling down the VMware certification route.
Whilst it has been time consuming, the effort has been worth it and has been rewarding both mentally and financially.
Now the VCAP-DCD is being retired immanently and replaced with the VCAP6-DCV Design (similarly the VCAP-DCA is being replaced with the VCAP6-DCV Deploy), effectively just a change in title for vSphere 6 with the blueprints updated.
Also be aware if your looking to do the VCAP to refresh your VCP, they have removed inheritance. If you are a VCP5, looking to do a VCAP in 6, you will refresh your VCP5, but not earn the VCP6.
I need to recertify come June, still not entirely sure how I'll be doing it. Probably take the delta to upgrade the VCP and look at the Deploy once I have that buffer.