What features should I look for in a laptop for virtualization-heavy workloads?

I think your problem has more to do with RAM than with CPU. If you can stuff more RAM in your laptop, it will go a long way. A good hypervisor can divide cpu time pretty well, but RAM has to be committed to specific VMs. After you max out RAM, look for more cores (ie: a slower-clocked quad core as opposed to a faster clocked dual core), so that each logical machine (including the host) can have at least one dedicated core. You also asked about a specific technology for better VM support. With the exception of certain netbook-class processors, any processor/motherboard on the market today will support these technologies, so odds are you're already doing everything you can there. However, these options sometimes are disabled by default in the BIOS/UEFI settings, to look there to make sure your virtualization features are actually enabled. Finally, running multiple VMs can sometimes create a lot of IO pressure, so a good SSD or RAID setup can often help considerably.

Most chips now have virtualization extensions (Intel-VT or AMD-V). From personal experience (VirtualBox), I can tell that some of the features -- especially nested paging -- are very helpful; nested paging, for example, lowers my Ubuntu boot time quite noticeably (from 45 seconds to 15 seconds).
(Edit: Seems like "nested paging" is also called "second-level address translation" or "extended page tables" [EPT].)

It also depends on what your development is. I tried compiling the Chromium source code on a Core i5 (no virtual machines at all, on an actual computer), and 4 GiB of RAM was not enough -- 6 GiB was almost enough, but I still needed ~1 GiB of pagefile to prevent running out of memory. (I normally turn off the page file.) Doing this on a VM was clearly out of the question on my system, mainly because of RAM (but also the CPU). So RAM is very important too, especially with 2 VM's, although it depends on what you're doing.

Another feature that might help is having a true dual-core (or more) laptop, having one VM run on one core and another on another core. I haven't tested the impact of this personally, though, since I usually only run one VM at any time.

Intel does have a virtualization technology called VT that provides an instruction set tailored specifically towards virtual machines. The Intel ARK has a list of VT capable processors. You'll find quite a few mobile processors there as well as desktop.