What's the best use of guild currency?

Yes. Get JE and swap him in for poggle. He is viable at 4*, G8. For the amount of guild currency you need to buy 50 salvage items, you can buy more than 200 shards. Get your JE to 5 or 6 stars before reconsidering buying gear. You can make an exception if you are close to completing an important part.

Also you might want to consider replacing GS with either a taunter or IG-100. With JE in your squad GS will be your slowest toon.

thanks! I have st han at 7*, lvl 76 so I'm thinking that would be a good sub for GS. will be sad to see GS go though haha

Max Rey or in your case, max JE. Both options are viable, personally I am going after Rey because she belongs to my Arena team and is 21 shards away from being maxed out.