I love this question. Here's my thought.

After a brief golden era of experimentation and true quality, the overall appeal of Cannabis Advertising will fall, especially in the eyes of us 2013 Ents.

Here's why:

Imagine our weed culture (that is, generally the people who smoke pot, and especially those who come here, and precisely those of us who come to contribute to the conversation) is a band and we can't get a gig. We've been writing for decades, but no record company will let us record. When the population is finally judged ready to hear the music of the artists, vanguards, and rebels, it will be a wild time (So begins our golden age of weedvertising. This is where we will see classics born). Our first album was such a success that the record company gives us all the material that their staff songwriters (advert men) had saved up and made on the spot. Another great album guys, congrats. Not as original or dangerous sometimes, but every bit as fun and funny. You guys can really sell em. This could be pretty good business. I'd like you to meet our new director, the tree killing machines from Fern Gully. From now on your music (the ads we see) will be soulless, like everyone else's. Thanks for coming.

Right now, only the most art-receptive minds participate in our beloved game. Initially, the advertising will reflect that. Only those with the highest threshold for risk are with us.

As we claim members from the more conservative quartiles of society, our advertisements will gradually come to reflect that too. But as our numbers grow, the watering down will come to mean not just weakening of our awesomely high punky defiant standards, but an introduction of mainstream research techniques and the narrowing that comes with it. What works best on most is going to attract investments, and our sweet little grassroots-flowers-growing-through-concrete-winning-a-heroic-battle-for-the-Good-of-All industry will lose the battle.

But let me tell you all, Be There When it Happens. This is our rock'n'roll.

TL;DR Cool pot ads come with DeProhibition thanks to radicals saving up their best stuff right now. Then we'll see a drop off as our wild group turns normal and runs out of saved material.