You can buy more warehouse space with credits. The DLC will only max it for money instead of sinking your credits.
DLC usually go on sales in winter and summer sales. Maybe in Easter, but I don’t know.
The DLC is usually the best bang for the buck considering the bonuses, the gold, and the premium ships. In fact I always recommend to buy at least the 4 smaller DLC instead of gold if you want to keep a license.
On sales, of course
PS: I think calling money grabbing the developers is not fair, since you can play for free. This is much better balanced than other F2P games.