30lb is too too much lift for a tropical, single-tank diver using minimal weight...
I do not really agree with this statement. 30 is not too much. It's probably more than is NEEDED. But, it's only too much if it creates some kind of problem.
I have the VDH 18 and the VDH 35. I can assure you that the VDH 35 is a great wing and you will not have ANY problems with it if you use it for tropical, single tank diving. I think the DGX wing is the same.
Think about what most tropical divers are using. Normal, integrated BCDs that most of them are using have as much as 45 pounds of lift. That does not cause a problem for any of them. The VDH 35 (and DGX 30) are well-designed wings and much smaller than those integrated BCDs.
Honestly, I suspect most people (including myself) probably could not tell any difference whatsoever in a blind test between diving the VDH 18 and the VDH 35.
I had the 35 first. I had absolutely no NEED for the 18. It is purely a luxury. I just WANTED it for a week of single tank, tropical diving that I had planned. It was great for that. But, I really cannot say that I would have been able to tell any difference in the water if I had had the 35.