I am considering a thigh lift because of loose skin/fat from weight loss. Could this help the venous insufficiency?

Unfortunately the thigh lift will not help with your venous insufficiency. It could make the problem worse! 
I actually recommend that any venous problems and varicose veins are addressed PRIOR to thigh lift surgery. Consult with a board certified plastic surgeon who can do a full evaluation and possibly collaborate with a vascular surgeon to study your case and give you the safest plan. Best wishes!

Thanks for your question, real60033.
Thigh lift is an elective cosmetic procedure that rarely has therapeutic effects, so this surgery will not really alleviate your chronic venous insufficiency. In fact, it might even worsen it.
Before thinking of getting thigh lift, make sure that you first get clearance from your licensed physician to ensure that you won’t compromise your health condition with the surgery.
Good luck!

Thanks for your question. The perforating veins affected in CVI are in the calves.  Therefore, a thigh lift will do little to help with this. However, the chafed and loosened inner thigh skin will be gone and may relieve the discomfort of this issue as a long term benefit. Have a consultation in person with a board certified plastic surgeon to see if you are a suitable candidate for thigh lift. Hope this helps.