I'll assume for the moment you mean the 50 gem 3* shards and 4 x 300k gold 3* shards unless you somehow can spend 250 gems per day on 3* shards in market? In terms of the 50 gem 3* shards, I certainly don't think it's worthwhile, if you are level 160+ for the level 8 hero shard event raid, you can spend 50 gems to get on average 39 3* shards and 39 4* shards including the chance to get double rewards, at that level, subtracting the three* s you use to fuse the 4* from the shards into 5*, you end up getting on average 1.3 extra 3* per 50 gems, so for 50 gems you get 0.1625 of a 5* hero, and also 1.3x3*hero.

However the 3* shards for gold are definitely worth it, the extra 4 a day helps a ton, and as they don't take up space, you can just save a load of the specific shards for when you need them.