If you have enough gold weapons then you should save them. I'm saving up to have at least 5k gold available at any time in case there is something that I want to buy with gold or if pix makes a mistake like what they did with the dragon bot offer on android (even though I am on iOS). The rest you can probably spend on instant upgrades.
Oops. Good thing I kept getting alot of silver every battle. Besides, my current hanger in Steam is Lvl 5 Carnage with 2 Exodus, Lvl 4 Butch with 2 Thunders and 2 Kang Dae, lvl 7 Fujin with 3 Vortexs, and lvl 10 Bolt with 3 MK II Pinatas. Powerful hanger, no?