It could be stronger both in idea and grammar. You don't want to insult your potential customers "only people without an imagination can't find a reason to drink champagne" assumes people are stupid. We might know they are, but they don't need to be told they are. Keep it light-hearted and omit any negatives...

My suggestion, consider the reasons that people drink Champagne. I'd say the majority do it to celebrate something.

So, approaching it as: "Any reason is a great reason to celebrate!"

Then in smaller text, you can say something like, "When you purchase a bottle of Moet & Chandon's from Ruby's, you can keep the celebration alive with a second bottle at a price worthy of your celebration." Expect cheapskates, and don't beg for more money. Omit the part about being generous.

In summary, most people are stupid and cheap, don't point it out. Approach it as a chance to bring in quality customers who will pay for a second bottle. So, make the idea appear smart and rich and smart, rich people will come.

Many thanks for your insightful comments Asvetic - I completely agree with your musings on the Wilde quote too, and I'll be offering it as an alternative to the client.

Dump the quote. If you’re going to do a simple all-copy ad then you should have one idea that can work as one block of text. If that block needs supporting copy the ad lacks confidence and feels desperate. It’s important to not give that impression because this ad amounts to a restaurant coupon which itself is a sign that the restaurant isn’t good enough to get by on the food and service and is using gimmicks to bring in business.

Understood James, thanks for the tip!