i have 18 pages of classic cards i have 7 classic legendary's
i was wondering if i should wait until the new expansion goes live or should i just buy classic packs because they never leave standard
Usually classic is a good advice for people who have small collections. 18 pages of only classic cards including 7 legendaries is a lot. You are likely to get a lot of dust out of those packs. Get the new expansion or, as some have suggested, Karazhan if you don't have it yet. Even considering that this expansion is leaving standard in about 17 month, its still a good choice. You are playing this game now, you might not even like it 17 month from now, and if you do you will have a larger colection and wild to look forward to.
If you haven't BRM and LOE and want to play wild in the future, purchase at least the first wing, maybe even everything. It still doesn't rotate out for a few months and there are some very good cards; althrough BRM Wing 1 is enough for now.
You should maybe save the money for the next adventure, not for the expansion. Iron rule to make the most out of money: buy expansions with gold, adventures with money.