The tavern pass is basically packaged cosmetics, with some increased gold gain as a bonus.
If you don't care about the cosmetics at all, you should ignore the tavern pass.
After some quick research, i want to alter this statement.
Depending on your playtime, you should probably buy the next tavern pass, as the 20% experience boost will most likely pay back enough gold to cover the cost and the added golden Legendary means the return surpasses the cost even if you ignore the cosmetics.
I would wait until some bundle turns up if I were you. If you're really low on cards it's understandable that you want to invest a bit, but maybe try to play some more arena and duels for trying out cards and earning extra gold. Tavern pass would have given you a good amount of gold, had you bought it two months ago, now the reward is basically halved. If you're up for playing your ass off, it might still pay off, but then again, 20€ will give you 20 packs and free legends when the offer comes. It's your money in the end
edit: The next expansion will be in 2 months at least, so there's still some time to kill. The mid expansion should be up rather soon, so maybe there will be a good opportunity to spend there :)