Am I missing out by not running in 64-bit mode?

Lion is not meant to be used in 32bit mode. Also addressing more than 4GB ram with 32bit kernel is slower (it uses PAE).

If the only reason of using Lion in 32bit mode is the Cisco VPN client (yuck!) there is a way. Here is an article explaining how to use the native VPN client instead - it's for 10.6, but should work. It's a matter of configuration, not of software. And here is a forum post that pointed to thad solution.

About the Cisco VPN 3000 hardware - yes, it works with iOS and native OSX VPN client in IPSec mode, and it's a matter of software update and configuration. You should be running at least 4.7.2P according to the CISCO field notice. It's stated that it's not supported, but it works. Here is another success story. Make sure that you're using at least OSX 10.7.2.

ps. being tight on money is not always bad, It usually makes people more creative and makes them think and learn new things. Direct your network admin to serverfault, a place I'm sure he will get decent help.

Not really - until you have programs that refuse to run on anything but a 64 bit kernel or programs that need to allocate more RAM than they can in 32 bit address space you can keep running 32 bit on the Mac OS.

Running a 32bit OS instance does not preclude you from running 64bit applications. It's one of the more unusual things about Mac OS X, and very different to the Windows way of doing things where there are specific 32bit/64bit versions with fairly rigid limitations on what you can run.

As such, depending what you use your computer for there are some disadvantages to running in 32bit mode (addressable memory as per a different answer for one) but by and large you are not forced to run everything in 32bit just because your kernel is, and so the disadvantages are considerable less than for other OS.

See the following question/answer on Stack Overflow for more details:

• https://superuser.com/a/100837

You can have a play with 32 and 64 bit versions of the kernel by looking at the following instructions from Apple*:

If your Mac uses the 32-bit kernel by default, but supports the 64-bit kernel, you can start up using the 64-bit kernel by holding the 6 and 4 keys during startup.

If your Mac uses the 64-bit kernel by default, you can start up with the 32-bit kernel by holding the 3 and 2 keys during startup.

Your Mac will revert to the default kernel the next time you reboot it.

To select the 64-bit kernel for the current startup disk, use the following command in Terminal:

sudo systemsetup -setkernelbootarchitecture x86_64

To select the 32-bit kernel for the current startup disk, use the following command in Terminal:

sudo systemsetup -setkernelbootarchitecture i386

Note: This setting is stored in the /Library/Preferences/SystemConfiguration/com.apple.Boot.plist file and will take effect every time you start up from this disk. If you start up from a different disk, the setting on that disk, or the hardware default, will take effect.

I am not sure why you talk about RAM in the middle of your question there, it doesn't seem particularly pertinent to me, and nor is there a specific question, so perhaps a question edit would be helpful to promote more answers.

(* Instructions for Snow Leopard, but should still apply)