Bump, And…
So I did some further testing, trying to narrow down where the issue existed, and in the process I think I may have found a couple defects...
The first issue is with the original problem in that I have not been able to get any traffic to route from VLAN214 - VLAN220 interface/networks to the WAN connection, given the configuration provided in my OP.
During my testing, I tried the following scenarios:
Scenario #1: Reduce # of VLAN interfaces from 8 to 3; (theory: pfSense cannot route traffic for >4 LAN interfaces)
Configuration: Same as what was documented in the OP, however I removed VLAN's #211, 212, 213. (reconfigured from factory default to maintain consistency in configuration comparison; VLAN214 = opt1, VLAN215 = opt2, etc..)
Result: Negative; issue still exists. I cannot ping the WAN GW from VLAN 214, 215, 216, etc. (though can still ping LAN GW, i.e. 10.0.215.10 -> 10.0.215.254).
Conclusion: The issue is NOT related to the number of interfaces which pfSense can route traffic for.
Scenario #2: Change the VLAN Tag of a working interface; (theory: pfSense has an issue with vlan tag ID's => 214; secondary theory: pfSense has an issue routing traffic from a /24 subnet that is => 214)
Configuration: Using configuration from OP as a starting point, I changed the VLAN tag ID of opt1 (VLAN211) to 214 keeping the original 211 wan IP address in the NAT/VIP config (wan.xxx.xxx.211). Removed original VLAN214 interface/configuration,VIP/NAT/FW rules to avoid conflicts.
Result: Positive; traffic can route OK.
Conclusion: pfSense has no issue with VLAN Tags => 214 or subnets equal or greater to the same number.
Scenario #3: Change the WAN VIP address of a working NAT config (VLAN211->wan.xxx.xxx.211) to one having an issue (VLAN211->wan.xxx.xxx.214); (theory: pfSense has an issue either with VIP's => 4 instances AND/OR VIP's => 214 (as in /32 address number))
Configuration: Using configuration from OP as a starting point, I changed the VIP/NAT config of opt1 (VLAN211) to use wan.xxx.xxx.214, and changed the VIP/NAT config of opt4 (VLAN214) to use wan.xxx.xxx.211.
Result: VLAN211 (using WAN IP 214) failed to route; VLAN215 is able to successfully route.
Conclusion: pfSense is having an issue routing NAT traffic to VIP WAN IP's =>214.
So.. Not sure where to go from here; unfortunately, I cannot get another /28 block of IP's from my ISP at this time that is below the hypothetical threshold/limitation I'm running into. In the interim this is figured out, I've had to scratch my VIP/NAT config entirely and have all 8 VLAN interfaces NAT to a single WAN IP (wan.xxx.xxx.210). Not ideal for the configuration I was hoping, but it works.
Is there anyone out there that would be willing to try and duplicate this issue? I'd like to confirm my sanity…
The second issue I found while I was testing is a rather nasty bug; I'll post it in another thread to avoid hijacking the purpose of identifying a solution to the original problem. (update: here's the other thread: http://forum.pfsense.org/index.php/topic,14940.0.html)