Looks like I am a bit late to the party, but great news. I have a large Vietnam collection already and only half painted.
Items I have found missing are decent looking civilians and VC dressed in city clothes which would be good for TET scenarios. Vehicle wise Sheridans, MUTTs, PBR's, bicycles, scooters etc. I have also found a lack of decent command type figures like radio operators and senior Officers for both sides. Of course these are on the extreme end of the wish list as the basics should be covered first.
When I started buying up vehicles the Corgi trucks, Helicopters and M48's were reasonably priced, but now days are extremely expensive and have been outbid many times. A new source of the vehicles would be welcomed I am sure.
Great to hear about AVRN being planned as I was going to use some of the smaller West Wind figures.