I read somewhere that one of the main disadvantages is that candidates for the veneers must be in good dental health before the procedure. (http://www.bestlosangelesdentist.com/lumineer-veneer.php)
How Much Decay Does It Take to Make Me a Bad Candidate for Lumineers?
Doctor Answers 2
All decay should be treated prior to Lumineer procedure
For any cosmetic procedure, including Lumineers to be successful long term, all decay and gum disease should be treated first. After the Lumineers are placed, it's also critical to maintain healthy teeth and gums by meticulous home hygiene and regular dental check ups and cleanings.
Dental decay should be eliminated before cosmetic treatment.
Your question is rather interesting. It's like saying how rotten should food be for us not to eat it? I'd simply say don't eat rotten food. To the same effect cosmetic treatment should be delayed until all active dental disease is dealt with. So no non or minimal prep Lumineers until you are decay free.